Child, Driesch's harmonic equipotential systems in form-regulation. 5^7 



Bildungen" or else they „soon die and are incapable of reparation". 

 According to Driesch's definition of regulation, it includes only 

 cases where a return or approach to the „normal" condition occurs 

 (Dries ch, 1901, p. 92), hence abnormal or atypical results are 

 unimportant. Nevertheless, I believe that these pieces present 

 certain problems of considerable importance: first, why does any 

 localization and development occur in pieces too short to form 

 wholes? second, why do partial structures of relatively large size 

 occur in some pieces, while others of the same length give rise to 

 wholes of smaller size? third, why do partial structures always 

 represent the distal portions of hydranths, never the proximal? 

 Driesch öfters no solution to these problems but says merely: 

 „klar ist nur, dass irgendwelche „innere Mittel" hier in Frage 

 kommen" (Driesch, 1908, p. 414). He does not even mention 

 my results and suggestions but refers merely to his and my own 

 „ziemlich wenig besagende Vermutungen". 



With respect to the regional occurence of partial and atypical 

 structures in the stem, Driesch says in this paper: „Sie tun es 

 nicht (i. e., they do not represent harmonic equipotential systems), 

 wenn sie gar zu jungem Gewebe entstammen, also dem Original- 

 stamm sehr weit distal entnommen sind" (Driesch, 1908, p. 414). 



In view of the fact that both Morgan and I have shown posi- 

 tively that stemless hydranths and partial structures may appear 

 in any region of the stem, provided the pieces are sufficiently short 

 (for literature see Child, 1907f), it is somewhat surprising to find 

 Driesch repeating his original views on this point without refe- 

 rence to the observations of others. If he has read my paper he 

 cannot be ignorant of the facts. Does he believe that the obser- 

 vations of Morgan and myself are incorrect or does he simply 

 prefer to ignore them? 



I have shown (Child, 1907 f) that there is a complete gradation 

 between results that Driesch regards as typical and the stemless 

 hydranth and distal partial hydranth. Shorter pieces are necessary 

 for the formation of partial structures and stemless hydranths in 

 the proximal than in the distal regions of the stem, and this fact 

 is correlated with the well known fact that shorter hydranths 

 appear in pieces from the proximal regions, whether the pieces 

 are long or short, than in pieces from the distal regions. In short, 

 there is every reason to believe that the same factors which give 

 rise to wholes in longer pieces give rise to the stemless hydranths 

 and the partial structures in the shorter pieces. 



To my mind the formation of distal partial structures and 

 stemless hydranths in very short pieces from any region of the 

 stem constitutes in itself a very serious objection to Driesch's 

 hypothesis: it is impossible, as Driesch practically admits, to under- 



