No. 627] 



ADAPTATION 



jected on account ol' the unusual and artificial character 

 of the operations, which could never have been provided 

 for by natural selection, nor, so far as we can see, by any 

 other recognized principle of evolution. The latter sup- 

 position is sufliciently disposed of by Driesch's analysis 

 (section III) and need not be considered here. 



Driesch admits that a physico-chemical machine ' ' might 

 very well be the motive force of organogenesis in gen- 

 eral, if only normal, that is to say, if only undisturbed 

 development existed, and if a taking away of parts of 

 our systems led to fragmental development" (IT, 139). 

 If, therefore, we can explain these critical cases without 

 invoking any principles beyond those believed to be oper- 

 ative in normal life-history, we have disposed of this line 

 of argument. 



In an earlier section of this paper I took the ground 

 that an adaptive or "purposive" response by the organ- 

 ism, if not guided by past individual or racial experience, 

 must be the result of experimentation. I avoided inten- 

 tionally at the time any consideration of tliose cases of 

 regeneration and form regulation in whicli tlie eiiu^r- 

 gency was totally new, and therefore lorcigii to llic 

 rience of the organism or its ancestors, i iciv ;i .-iMcinlly 

 evolved mechanism could hardly be invoked. 1 

 gested, how^ever, that the principle of ''trial aud oi-ror" 

 could be applied to these cases: This suggestion was, of 

 course, not new. Such an extension of this conception 

 had already been made by Jennings,^'' though it is rather 

 surprising to note that he has given it little further con- 

 sideration in his recent discussions of vitalism. For, to 

 my mind, an explanation involving this principle, seems 

 the only alternative at present to a vitalistic one, or, 

 better stated, it seems to me the only alternative to an 

 abandonment of the search for a scientific explanation. 



According to the trial and error prinei ])](>, as applied 

 to the movements of a lower animal, "heliavior that re- 

 sults in interference with tlie noi'inal !th'tal)olif pr.H-,-M>s 



