SUMMARY OF PHYSIOLOGICAL EEVELOPMEM. 387 



tions. Direct equilibration in organisms, with all its accom- 

 panying structural alterations, is as certain as is that uni- 

 versal progress towards equilibrium of which it forms part. 

 And just as certain is that indirect equilibration in organisms 

 }o which the remaining large class of differentiations is due. 

 The development of favourable variations by the killing of 

 individuals in which they do not occur or are least marked, 

 is, as before, a balancing between certain local structures and 

 the forces they are exposed to ; and is no less inevitable than 

 the other. 



314. In all which universal laws, we find ourselves again 

 brought down to the persistence of force, as the deepest 

 knowable cause of those modifications which constitute 

 physiological development ; as it is the deepest knowable 

 cause of all other evolution. Here, as elsewhere, the per- 

 petual lapse from less to greater heterogeneity, the perpetual 

 begetting of secondary modifications by each primary modi- 

 fication, and the perpetual approach to a temporary balance 

 on the way towards a final balance, are necessary implica- 

 tions of the ultimate fact that force cannot disappear, but 

 can only change its form. 



It is an unquestionable deduction from the persistence of 

 force, that in every individual organism each new incident 

 force must work its equivalent of change ; and that where it 

 is a constant or recurrent force, the limit of the change it 

 works must be an adaptation of structure such as opposes to 

 the new outer force an equal inner force. The only thing 

 open to question is, whether such re -adjustment is inherit- 

 able ; and further consideration will, I think, show, that to 

 say it is not inheritable is indirectly to say that force does 

 not persist. If all parts of an organism have their func- 

 tions co ordinated into a moving equilibrium, such that every 

 part perpetually influences all other parts, and cannot be 

 changed without initiating changes in ail other parts if the 

 limit of change is the establishment of a complete harmony 



