Physiological Basis of Restitution of Lost Parts 487 



I cannot see that anything is gained by the use of this term. More- 

 over, it seems to me that many of the correlations are not really 

 symbiotic at all, except in so far as they may be mutual with 

 respect to complex parts of the organism. For example, the mere 

 mechanical union with other parts is undoubtedly in many cases 

 one factor in preventing parts of the organism from undergoing 

 regulation into wholes. But I cannot see that it serves any useful 

 purpose to call such factors symbiotic relations. It seems pref- 

 erable therefore to maintain that these relations, or as I believe 

 we may more properly call them, correlations, are physically and 

 chemically of all sorts possible in the material and environment 

 in which they exist. Moreover, while many of them are undoubt- 

 edly mutual, i. e., reciprocal, at least as regards complex parts, 

 others are just as certainly largely or wholly one-sided so far as 

 form is concerned. It seems scarcely necessary to enlarge further 

 upon this point. As regards the existence of relations between 

 parts as an essential feature of regulation Holmes and I agree 

 perfectly. As regards form-regulation we differ, in that it seems 

 to me difficult or impossible to account for the facts on the basis 

 of symbiotic relations, even in the widest sense. 



Holmes' illustration of the process of regeneration is as follows : 

 "Let us imagine an organism made up of a number of differen- 

 tiated cells, each of which derives some advantage from some 

 substances produced by the contiguous cells, and giving out some 

 substance upon which the contiguous cells are more or less depend- 

 ent. We will suppose that in addition to these differentiated cells, 

 there are scattered through the body numerous indifferent or 

 embryonic cells whose multiplication is held in check by the others, 

 but which upon the removal of any part respond to the functional 

 disturbance by growth and multiplication near the place of muti- 

 lation. We may represent our organism by the following diagram 

 in which the differentiated cells are represented by the larger 

 circles A, B, C, etc., and the indifferent cells by the smaller circles 

 betw^een them. Each cell such as A contributes something util- 

 ized by B, G, and F, and derives something in return from each 

 of these sources. Now suppose A is removed: the indifferent 

 cell lying nearby, no longer held in check by the same stimuli, 



