HEREDITY. 319 



be altered without causing alterations of action and struc- 

 ture in all the rest; just as no member of the Solar System 

 could be modified in motion or mass, without producing re- 

 arrangements throughout the whole Solar System. And if 

 the organism A, when changed to A', must be changed, in all 

 its functions; then the offspring of A' cannot be the same 

 as they would have been had it retained the form A. That 

 the change in the offspring must, other things equal, be in 

 the same direction as the change in the parent, appears 

 implied by the fact that the change propagated throughout 

 the parental system is a change towards a new state of 

 equilibrium — a change tending to bring the actions of all 

 organs, reproductive included, into harmony with these new 

 actions. Or, bringing the question to its ultimate and sim- 

 plest form, we may say that as, on the one hand, physiological 

 units will, because of their special polarities, build them- 

 selves into an organism of a special structure; so, on the 

 other hand, if the structure of this organism is modified 

 by modified function, it will impress some corresponding 

 modification on the structures and polarities of its units. The 

 units and the aggregate must act and re-act on each other. 

 If nothing prevents, the units will mould the aggregate into 

 a form in equilibrium with their pre-existing polarities. If, 

 contrariwise, the aggregate is made by incident actions to 

 take a new form, its forces must tend to re-mould the units 

 into harmony with this new form. And to say that the 

 physiological units are in any degree so re-moulded as to 

 bring their polar forces towards equilibrium with the forces of 

 the modified aggregate, is to say that when separated in the 

 shape of reproductive centres, these units will tend to build 

 themselves up into an aggregate modified in the same direc- 

 tion. 



Note. — A large amount of additional evidence supporting 

 the belief that functionally produced modifications are in- 

 herited, will be found in Appendix B. 



