288 PHYSICAL EXPRESSION. 



When growth is found to be good or bad in one 

 part of a subject, it often happens to be similarly 

 good or bad in other parts ; this is termed the 

 principle of similar development The similarity is 

 as to kind. In some cases this similarity as to kind 

 is explicable, in other cases it is empirical. This 

 principle is the basis of what are termed the 

 " temperaments, or diathesis," in medicine. 



One object of the analysis given, and the enun- 

 ciation of principles in this chapter, is to show the 

 usefulness of analogy between a series of move- 

 ments and a series of trophic actions. A series of 

 movements may be compared with the normal, as 

 easily as a series of measurements is compared 

 with fixed tables of the normal measurements. 

 The expressions of development may be described 

 in terms of series of kinetic and trophic actions ; 

 this is illustrated by examples. 



Probably it may be demonstrated that forces 

 afferent to the subject may bring about special 

 combinations end sequences of trophic and kinetic 

 action. I imagine that here we have an important 

 factor in the process of evolution of the individual 

 and of the species. A subject, as the result of vital 

 action, may display two or more functions say, 

 trophic and kinetic action ; the relative proportion 

 of the two may vary in quantity thus the total 

 function of the subject may appear to vary in 

 kind : all this may result from the action of afferent 

 forces. 



Some of the principles concerned in heredity 

 may be illustrated by the principles enunciated in 

 this chapter. 



