490 C. M. Child 



In this case the undifferentiated material which in the absence of 

 A is stimulated to develop, will develop into another A. But in 

 this case the relation between the original A and the other parts 

 of the system is essentially one-sided and not mutual or sym- 

 biotic. Or as a second possibility, we may assume that the rela- 

 tion between A and the other parts of the system is such that 

 removal of A produces modifications in the other parts only very 

 slowly, while in the absence of ^ these other parts affect the undif- 

 ferentiated cells in such manner as to bring about rapid develop- 

 ment so that restoration is complete before the parts B, G, F, etc., 

 have been appreciably altered by the absence of A . Here the 

 relations, though in the final analysis mutual, are so far as A and 

 its restoration are concerned, one-sided. In short, if we accept 

 the symbiotic theory as a basis, we can account for the restoration 

 of a part like that removed only by additional assumptions, accord- 

 ing to which the relations involved in the restoration become prac- 

 tically one-sided rather than mutual. 



In my earlier criticism of Holmes' theory (Child 'o6a, pp. 420, 

 421) the following statement appears: "To return to Holmes' 

 diagram, replacement of A can occur only when the relation is 

 largely one-sided, i. e., when A is dependent on B-F, but these 

 latter are not to any marked degree dependent on A . In this case, 

 and in this case only, will the "social pressure" force the undif- 

 ferentiated cell to differentiate into something like A." 



Holmes rephes to this: "Where redifferentiation from new 

 tissue is concerned, as in the present case, it is not the relation of 

 A to B-F, that should be more or less one-sided, but the relation 

 of the tissue in place of y^ to this complex. This is an important 

 distinction which Child does not seem to have considered. B-F 

 are relatively fixed, the tissue in place of y^ is young and plastic, 

 and more dependent so far as the direction of its differentiation 

 is concerned, upon B-F, than these are upon it. We may grant 

 that when regeneration occurs, the relation of dependence between 

 the old parts and the new tissue is more or less one-sided, although 

 the relations of the part removed may not have been. This would 

 naturally result if the parts were relatively stable. They may be 

 in a symbiotic relation, nevertheless, each part contributing in 



