444 The American Naturalist. [June, 



struction, the lessons of pleasure and pain, and of experience 

 generally, and reasoning from means to ends, etc. 

 We reach, therefore, the following scheme : 



Ontogenetic Modifications. Ontogen-ic Agencies. 



1. Physico-genetic 1. Mechanical. 



2. Neuro-genetic 2. Nervous. 



3. Psycho-genetic 3. Intelligent. 



Pleasure and pain. 

 Reasoning. 



Now it is evident that there are two very distinct questions 

 which come up as soon as we admit modifications of function 

 and of structure in ontogenetic development : first, there is the 

 question as to how these modifications can come to be adap- 

 tive in the life of the individual creature. Or in other words : 

 What is the method of the individual's growth and adapta- 

 tion as shown in the well known law of " use and disuse ? " 

 Looked at functionally, we see that the organism manages 

 somehow to accommodate itself to conditions which are favor- 

 able, to repeat movements which are adaptive, and so to grow 

 by the principle of use. This involves some sort of selection, 

 from the actual ontogenetic variations, of certain ones — certain 

 functions, etc. Certain other possible and actual functions and 

 structures decay from disuse. Whatever the method of doing 

 this may be, we may simply, at this point, claim the law of 

 use and disuse, as applicable in ontogenetic development, and 

 apply the phrase, " Organic Selection," to the organism's be- 

 havior in acquiring new modes or modifications of adaptive 

 function with its influence of structure. The question of the 

 method of " Organic Selection " is taken up below (IV) ; here, 

 I may repeat, we simply assume what every one admits in 

 some form, that such adaptations of function — " accommoda- 

 tions" the psychologist calls them, the processes of learning 

 new movements, etc. — do occur. We then reach another ques- 

 tion, second ; what place these adaptations have in the gen- 

 eral theory of development. 



Effects of Organic Selection, — First, we may note the results 

 of this principle in the creature's own private life. 



