66 MENTAL EVOLUTIOX IX ANIMALS. 



levels with which alone the present essay is to be concerned, if 

 we pitch upon any one of them at random, we shall obtain a 

 certain rough estimate of the grade of mental evolution which 

 is presented by the animals named upon that level. 



To avoid misapprehension I may add that in thus render- 

 ing a diagrammatic representation of the probable course of 

 mental evolution with the comparisons of psychological 

 development exhibited in the parallel columns, I do not 

 suppose that the representation is more than a rough or 

 general outline of the facts; and, indeed, I have only 

 resorted to the expedient of thus representing the latter for 

 the sake of convenience in my subsequent discussion. Eough 

 as this outline of historical psychology may be, it will serve 

 its purpose if it tends to facilitate the exposition of evidence, 

 and afterwards serves as a dictionary of reference to the more 

 important of the facts which I hope this evidence will be able 

 to substantiate. 



Such being the general use to which I intend to put the 

 diagram, I may here most fitly make this general remark in 

 regard to it. In the case alike of the stem, l^ranches, and the 

 two parallel columns on either side — i.e., all the parts of the 

 diagram which serve to denote psychological faculties — we 

 must remember that they are diagrammatic rather than truly 

 representative. For in nature it is as a matter of fact impos- 

 sible to determine any hard and fast lines between the com- 

 pleted development of one faculty and the first origin of the 

 next succeeding faculty. The passage from one faculty to 

 another is throughout of that gradual kind which is charac- 

 teristic of evolution in general, and which, while never pre- 

 venting an eventual distinction of species, always renders it 

 impossible to draw a line and say — Here species A ends and 

 species B begins. Moreover, I cannot too emphatically im- 

 press my conviction that any psychological classification of 

 faculties, however serviceable it may be for purposes of 

 analysis and discussion, must necessarily be artificial. It 

 would, in my opinion, be a most erroneous view to take of 

 Mind to regard it as really made up of a certain number of 

 distinct faculties — as erroneous, for example, as it would be 

 to regard the body as made up of tlie faculties of nutrition, 

 excitability, generation, and so on. All such distinctions are 

 useful only for the purposes of analysis ; they are abstractions 

 of our own making for our own convenience, and not 



