36 C. M. CHILD. 



the known phenomena of inheritance can be far more readily 

 accounted for on the basis of different dynamic equilibria. If 

 the organism is a dynamic system, changes in its constitution 

 or in the conditions of the environment may alter its equilib- 

 rium and such changes may become evident, now in this char- 

 acter now in that or in a group of characters, according to the 

 nature of the organism and the conditions concerned. There 

 is absolutely no reason for supposing that a localized morpho- 

 logical character must be represented by a localized unit or 

 entity of any sort. It may be and undoubtedly is simply a 

 local manifestation of a condition pertaining to the organism 

 as a whole. How can we doubt, for instance, that the color 

 characteristics which have played so important a part in many 

 Mendelian experiments are dependent upon the metabolism of 

 the organism as a whole, rather than upon independent units 

 existing in a hypothetical germ plasm. In the course of my own 

 work on Planaria I have been able to demonstrate that the 

 number, size and localization of such definite and sharply localized 

 characters as the eyes are dependent upon, and vary with quan- 

 titative metabolic conditions existing in the whole organism or 

 piece. 



The germ plasm hypothesis gives us no help at any point. 

 The facts can be more readily interpreted without it than with 

 its aid : in fact it does not serve as a basis for analysis but merely 

 affords us a means of paraphrasing the facts of observation 

 into terms of absolutely unknown quantities. Why should 

 biology continue to burden itself with this mass of speculation 

 which affords no basis for real progress? 



But if heredity is not the genetic history of the germ plasm 

 or its determinants or unit characters, how then shall we define 

 it? In the first place, we must admit, I believe, that wherever 

 reproduction of any kind, whether of parts or of wholes, occurs, 

 there we have also to do with heredity. And secondly, the 

 facts seem to me to show that we are concerned in heredity 

 rather with capacities, with potentialities, than with continu- 

 ously existent entities. And finally, there is much evidence 

 which indicates that these capacities and potentialities exist 

 simply in the sum total of the dynamic processes which are 



