Child, Driesch's harmonic equipotential systems in form-regulation. (315 



see that facts may become of relatively slight importance in the 

 light of such conceptions, for facts can neither prove nor disprove 

 their correctness. But it is also easy to see that these conceptions 

 do not afford a basis for „proof" of the „Autonomie der Lebens- 

 vorgänge", for while the facts can be interpreted in this way, such 

 interpretation is far from necessary. The sea-urchin egg, for example, 

 is not a harmonic equipotential system along the polar axis in fact, 

 but merely ex hypothesi. 



In his various discussions of harmonic equipotential systems 

 Dries ch has referred repeatedly to Planaria as constituting such 

 a system. In connection with these references it is stated that 

 „regeneration" in the stricter sense does not occur or is very slight 

 in Planaria. For example, he says that „eigentliche Regenerations- 

 erscheinungen — hier gerade nicht vorliegen" (Driesch, 1899a, 

 p. 54), and again „wird eine Planaria der Quere nach in Stücke 

 geschnitten, und wird dann eines der Operationsprodukte kontinuier- 

 licher Beobachtung unterzogen, so sieht man, wie an diesem Stück 

 neue Wachstumsvorgänge nur in ganz geringem Maße auftreten — 

 leider gestattet die Natur des Objektes eine intimere histologische 

 Untersuchung nicht" (Driesch, 1899a, p. 55). And in a later paper 

 (1901, pp. 180 — 181) he again speaks of the „geringfügige Regene- 

 rationsprozesse." 



It is of course a matter of personal opinion as to what the 

 limits of „geringfügige Regenerationsprozesse" may be, but Driesch's 

 assertion quoted above, that eigentliche Regenerationserscheinungen 

 — • hier nicht vorliegen" is certainly incorrect. Examination of the 

 living animals shows very clearly the formation of an „Anlage" 

 composed of new tissue formed at the cut surface and this under- 

 goes gradual differentiation. Moreover, Flexner (1898) found 

 abundant mitosis in the region of the cut surface: in Morgan's 

 work (1898, 1900, 1901) it is sufficiently clear that at least the 

 terminal regions of the parts removed are replaced by new tissue 

 in all cases. Bardeen (1902) found both mitosis and amitosis 

 involved in the development of the new tissue, and I have been 

 able to confirm his results (Child, 1907 h). It is also clear from 

 the work of Morgan and other later investigators that the whole 

 head and often a considerable region posterior to it and in many 

 cases almost the whole, in short pieces from the anterior region 

 the whole, of the postpharyngeal region, i. e., half of the body, 

 are formed by true regeneration in Driesch's sense. And finally, 

 Driesch's assertion that the nature of the object does not permit 

 a more exact histological investigation is certainly far from correct, 

 for as a matter of fact it is not in the least difficult to determine 

 that there is really very little „Substanzverlagerung" so far as 

 actual cells are concerned, though of course a transfer of substances 



