42 MENTAL EVOLUTION IN ANIMALS. 



are, after a time, cemented with all the firmness of the 

 strongest instinct." 



Precisely analogous to this process of blending many 

 separate muscular movements into one simultaneous and com- 

 pounded movement, is the process of blending many simple 

 ideas into one complex or compounded idea. Just as mus- 

 cular co-ordination is dependent on the simultaneous action 

 of a certain group of nerve-centres for the purpose of securing 

 the combined action of a number of muscles, so we must 

 suppose that a general or a composite idea is dependent on 

 the simultaneous activity of several nerve-centres which 

 minister to the several component parts of the blended idea. 

 The psychological side of this process has been so well ex- 

 pressed by James Mill, that I cannot do better than render it 

 in his words : — " Ideas which have been so often conjoined 

 that whenever one exists in the mind the other exists along 

 with it, seem to run into one another, to coalesce, as it were, 

 and out of many to form one idea, which idea, however, in 

 reality complex, appears to be no less simple than any one of 



those of which it is compounded The word 



' gold,' for example, or the word ' iron,' appears to express as 

 simple an idea as the word ' colour,' or the word ' sound.' 

 Yet it is immediately seen that the idea of each of those 

 metals is made up of the separate ideas of several sensa- 

 tions : colour, hardness, extension, weight. Those ideas, how- 

 ever, present themselves in such intimate union, that they 

 are constantly spoken of as one, not many. We say, our 

 idea of iron, our idea of gold ; and it is only with an effort 

 that reflecting men perform the decomposition." And simi- 

 larly, of course, with the most highly complex ideas, except 

 that the more complex they become the greater is the diffi- 

 culty of securing the needful composition, and the more easily 

 do they undergo disintegration. Thus it is that, in the words 

 of Mr. Spencer, " In the development of mind there is a pro- 

 gressive consolidation of states of consciousness. States of 

 consciousness once separate become indissoluble. Other states 

 that were originally united with difficulty, grow so coherent 

 as to follow one another without difficulty. And thus there 

 arise large aggregations of states, answering to complex 

 external things — animals, men, buildings — which are so 

 welded together as to be practically single states. But this 

 integration, by uniting a large number of related sensations 



