58G Child, Driesch's harmonic equipotential systems in form-regulation. 



and misiinderstanding somewhat less effective than they might 

 otherwise be. 



As regards my „reaction energy" (See Child, 1907b, 1907 d: 

 Driesch, 1908, pp. 414—415), it is perhaps not far removed from 

 the facts as Driesch's „entelechie". 



Driesch (1899b, pp. 120 — 121) has attempted to explain teleo- 

 logically the proportional decrease in length of the primordium with 

 decrease in the length of the piece. His explanation is essentially, 

 that the new hydranth must posses a stem in order to emerge 

 from the perisarc, and that it is also „zweckmäßig" that a region 

 capable of future „reparation" should be present. Consequently 

 when the piece is to short to permit the formation of a hydranth- 

 primordium of full length and also a stem, the length of the pri- 

 mordium decreases. But, as the measurements — both Driesch's 

 and my own — show, the shorter the piece the less the relative 

 length of the stem proximal to the hydranth. Consequently in 

 pieces sufficiently short, we may expect to find hydranths alone 

 produced, without any stem, or even distal parts of a hydranth 

 without proximal portions. All who are familiar with the pheno- 

 mena of regulation in short pieces in Tubularia know that very 

 short pieces do actually produce structures of these kinds. In short 

 the phenomena in longer pieces with decreasing length foreshadow 

 those which occur in very short pieces. Driesch disposes of the 

 phenomena in very short pieces as follows: „In der Tat unterbleibt 

 ja, wie früher geschildert, bei sehr weit oralwärts dem ursprüng- 

 lichen Individuum entnommenen Stückchen, die sich sehr rasch 

 reparieren, jene quantitative Regulation: aber was resultiert daraus? 

 eine durchaus atypische Bildung oder zwar ein ganzer Kopf, der 

 aber wegen fehlenden oder zu kleinen Streckstückes nicht aus dem 

 Perisark frei wird, oder auch, wenn er etwa durch die Bewegungen 

 seiner Tentakeln sich frei macht, bald abstirbt und keine reparative 

 Potenzen besitzt" (1899 b, p. 121). These are results which we do 

 not „teleologisch sehr wohl verstehen", but this apparently is of 

 no importance to Driesch, for they are either „ganz atypische 



5 mm with pieces 1,5, 2 and 2,5 mm in length without separating the different 

 absolute lengths. But since the decrease in length of the primordium depends in 

 part upon the absolute lengths of the pieces compared and not merely upon their 

 relative lengths, Driesch's measurements give simply average results for relative 

 decrease of 50 ''/o in pieces of different absolute length. Consequently his figures, 

 when treated in the same way as my own show in general greater decreases in the 

 lengths of the primordia for a given decrease in the length of the pieces (Child, 

 1907, p. 189. Compare Tables III and IV). If he had compared pieces of a single 

 given length with pieces of another given length his actual percentages would have 

 been different and much nearer my own, and he would not have found that the 

 decrease in the length of the primordium was 50 "/o in pieces double the length of 

 the typical primordium, but much less than that. 



