Physiological Basis of Restitution of Lost Parts 501 



To sum up: Holmes and I agree in that we both postulate a 

 condition of physiological equilibrium, or rather, as I should put 

 it a condition of oscillation or cyclical change about equilibrium, 

 as the basis of our hypotheses. The chief point of difference between 

 us is that Holmes' hypothesis does not, as I understand it, provide 

 for the maintenance of or return to the typical condition, except by 

 the assumption of relations largely one-sided, or that of lack of 

 plasticity. While these assumptions may serve for certain indivi- 

 dual cases, they seem to me to be totally inadequate for the analysis 

 of form-regulation in general. According to my own hypothesis 

 a part can be replaced only when some other part is physiologi- 

 cally sufficiently similar to it to perform its functions at least 

 qualitatively, if not quantitatively, after its removal. 



The independent formulation of two hypotheses of form-regu- 

 lation so similar in general point of view as are Holmes' and my 

 own, is I believe not without significance, since agreement between 

 different observers as regards the general nature of problems may 

 be an indication that real progress in the analysis of data is being 

 made. It is desirable in such cases, and particularly in fields 

 where the data are so varied and complex, that differences of 

 opinion should be fully and critically discussed. For this reason 

 I have ventured to consider at some length in the present paper 

 the points which seem to me debatable, and to state my own posi- 

 tion in a manner which I hope will lessen the chances of future 

 misunderstanding. 



Hull Zoological Laboratory 



University of Chicago 



February', looS 



