EXPLANATION OF THE DIAGRAM. 65 



_ce£tion, and then continues in its own line of development to 

 a somewhat higher level. Similarly, Imagination arises out 

 of Perception, and so with all the other branches. Thus, the 

 fifty levels which are drawn across the diagram are intended 

 to represent degrees of elaboration ; they are not intended to 

 represent intervals of time. Such being the case, the various 

 products of mental evolution are placed in parallel columns 

 upon these various levels, so as to exJnbit the comparative 

 degrees of elaboration, or evolution, which they severally 

 present. One of these columns is devoted to the psycho- 

 logical scale of intellectual faculties, and another to the 

 psychological scale of the emotional. But for the danger of 

 rendering the diagram confused, these faculties might have 

 been represented as secondary branches of the psychological 

 tree ; in a model this might well be done, but in a diagram it 

 would not be practicable, and therefore I have restricted the 

 branching structure to represent only the most generic or 

 fundamental of the psychological faculties, and relegated those 

 of more specific or secondary value to the parallel columns on 

 either side of the branching structure. In these two columns 

 I have throughout written the name of the faculty at 

 what I conceive to be the earliest stage, or lowest level of its 

 elaboration ; i.e., where it first gives evidence of its existence. 

 In another parallel column I have given the grades of mental 

 evolution which I take to be characteristic of sundr}^ groups 

 in the animal kingdom, and in yet another column I have 

 represented the grades of mental evolution which I take to 

 be characteristic of different ages in the life of an infant. 



In my subsequent work I shall fill up all the levels in 

 these vertical columns which are now left blank, on account 

 of the text of the present work being restricted to the mental 

 evolution of animals. At first I intended in this work to 

 truncate the whole diagram at the level where mental evolu- 

 tion in animals ends — i.e., at the level marked 28 — and to 

 reserve the continuation of the stem and branches, as well as 

 that of the parallel colunnis, for my ensuing work. But 

 afterwards I thought it was better to supply the continuation 

 of the stem and branches, in order to show the proportion 

 which I conceive to obtain between the elaboration of the 

 liigher faculties as they occur in animals and the same 

 faculties as they occur in man. 



Confining, then, our attention to the first twenty-eight 



F 



