6 j 6 Child, Driesch's harmonic equipotential systems in form-regulation. 



in the form of nutrition does occur. Even the new pharynx, when 

 formed in the old tissue, as is commonly the case, is the result 

 of localized cell division, at first chiefly mitotic, later chiefly ami- 

 totic, i. e., even in this case an „Anlage" is formed by cell division 

 and later undergoes differentiation. In her recent paper on this 

 subject Stevens (1907) has assumed that cell migration occurs 

 extensively in addition to cell division. Steinmann (1908) has 

 pointed out the insufficiency of her evidence for cell migration, 

 and since frequent cell division has been observed by Flexner, 

 Bardeen and myself the assumption of cell migration is un- 

 necessary. 



But, leaving these later results out of consideration, it was 

 sufficiently evident from the earlier work that regeneration is an 

 important factor in regulation in Planaria. 



This particular case has constituted a considerable difficulty 

 to me in my attempts to obtain a clear idea of Driesch's exact 

 conception of the harmonic equipotential system. In my work on 

 Cerianthus, I decided after some hesitation that, so far as the 

 occurrence of true regeneration was concerned, this form correspon- 

 ded as - closely to Driesch's of harmonic equipotential systems 

 general definitions as did Planaria, since in Cerianthus the actual 

 amount of regeneration is under most conditions proportionally 

 much less than in Planaria. I therefore called attention to the 

 fact that as regards proportionality Cerianthus does not correspond 

 to Driesch's definition since proportionality is not maintained with 

 decrease in size of the piece (Child, 1905). In one of his reviews 

 of literature Dries ch says concerning this work: „Wir glauben 

 zwar vornehmlich in seinen Beobachtungen an Cerianthus, bei dem 

 anfänglich unproportionale Regenerate in ihrem zu dicken Stamm- 

 abschnitt allmählich dünner und länger w^erden, doch Restitutionen 

 unseren Sinnes erblicken zu müssen" (Driesch, 1905 b, p. 68). 

 This Statement appears in a section devoted to the couvsideration 

 of harmonic equipotential systems, and so far as I can see, means 

 that Driesch regards Cerianthus as a harmonic equipotential 

 system. But elsew^here in the same paper he says that „Child 

 den .analytischen Begriff des harmonisch-äquipotentiellen Systems 

 gänzlich miss verstanden hat, wenn er in der Meinung, diesen 

 Begriff ad absurdum zu führen, beibringt, dass Cerianthus von 

 Bruchstücken aus, umbekümmert um deren Größe, gleiche Anteile 

 nach beiden Richtungen regeneriere, dass also keine Proportion 

 zwischen Stamm und Regenerat bestehe. Bei allen Regenerationen 

 handelt es sich ja eben um komplex-äquipotentielle Systeme in 

 meinem Sinne" (Driesch, 1905, p. 791). Later I attempted to defend 

 my position by comparing Cerianthus with Planaria (Child, 1907e, 

 pp. 140 — 141), and to this Driesch has again replied: „Ich habe 



