Child, Driesch's harmonic equipotential systems in form regulation. 581 



the wounded surface at one end and that the tentacle-ridges, which 

 are the most conspicuous parts of the hydranth-primordium do not 

 arise at the cut surface, but the distal end of the hydranth is at 

 the cut surface in all cases. If Driesch's conclusion is justifiable 

 on the basis of these facts then we are justified in concluding that 

 every scientific problem which is at present unsolved is elementary 

 in nature. 



But let us examine the case of Tubularia somewhat more fully, 

 in order to determine whether possible factors of localization exist, 

 and whether any of the data of experiment afford any evidence 

 with regard to such factors. In the first place, every piece which 

 is capable of becoming a new whole possesses some degree of 

 polarity, and experimental data indicate that this polarity consists 

 in differentiation or specification along the axis (Child, 1907g): 

 in Tubularia polarity disappears completely so far as morphogenesis 

 is concerned in pieces below a certain size. There is no ground 

 for believing that polarity is a fundamental property of protoplasm 

 and that each element or particle possesses it. If polarity is simply 

 axial difference in specification or in correlation of parts, then it 

 may afford a basis for localization, though perhaps insufficient alone 

 to account for all details. 



Secondly, the act of separation establishes a new „end" or 

 terminal region and the new hydranth forms at this end. The tip 

 of the manubrium coincides in position with the end of the piece. 

 The first visible changes leading to the formation of a new hydranth 

 begin at the end, and the phenomena in short pieces suggest that 

 the various parts of the new whole are localized in succession, 

 beginning at the end (Child, 1907 d, 19071'). For Driesch these 

 small pieces which give rise to partial structures are simply 

 „atypical", a sort of „freak of nature" and can teach us nothing 

 concerning „normal" phenomena. But if we attempt to analyse 

 the process of morphogenesis in Tubularia on the basis of all the 

 phenomena instead of a part^ the assertion that the elementary 

 nature of the problem appears clearly becomes, even with our 

 present knowledge, almost absurd. 



The possible „mechanistic" factors involved in the formation of 

 a whole from a part are therefore, when reduced to the lowest 

 termes: first, the constitution of the piece and the regional diffe- 

 rences which exist in it in consequence of its previous differentiation 

 as a part of an organism; second, the internal changes which result 

 from its isolation, i. e., from the cessation of the action of other 

 parts upon it, and these are undoubtedly different in different 

 regions; third, the changes in relation to the extra-organic environ- 

 mant, resulting from formation of terminal regions by the act of 

 separation, or the exposure of new surfaces to direct contact with 



