XXXIII.] MENTAL DEVELOPMENT. 67 



which all mind is developed ; and in the next, that con- 

 sciousness has its separate root in sensation, thought in 

 vital intelligence, and will in motor action. I reply that 

 no such expression can be anything more than a metaphor, 

 and that the truths indicated by the metaphors do not 

 contradict each other, but supplement each other. Had 

 they been indicated by inconsistent metaphors it would 

 not have mattered, but it may be shown, if it is worth 

 showing, that the metaphors are really consistent with 

 each other. We may say that consciousness, thought, and Relation 

 will are all developed out of the single germ of sensation, °iji^°^if^^ 

 but thought and will send down each its own root into the to the 

 insentient life ; thought into unconscious vital intelligence, jj^^P^'^ti'''^* 

 will into the motor function. 



I have a few more remarks to make before going on to 

 trace the details of the process by which mind is deve- 

 loped out of the germ of sensation. 



All development, mental as well as bodily, is differentia- 

 tion ; and in describing any process of differentiation, it is 

 difl&cult, if not impossible, to avoid the use of language 

 which will appear to imply that differentiation signifies 

 hranching oiit. Especially is this true when the successive 

 differentiations are stated in a tabular form. In the tabular 

 form to which I intend to reduce the summary of this 

 subject, it will necessarily appear as if the various mental 

 functions branched out of sensation, as the branches of 

 a tree out of its root. But this, though of course only 

 metaphorical, would be a most inaccurate metaphor. The 

 true analogy to the differentiations that constitute mental 

 development does not consist in the separation of the 

 branches of a tree, which are all alike in functions and 

 in organization. The true analogy is in that differentiation Analogy of 

 of unlike parts from each other which takes place in the ^^'^^^^} *" 



■] , '^ organic 



development of all organisms, and most completely in the develop- 

 highest. The differentiated organs and tissues of organisms ^^^^^' 

 do not branch out and separate ; on the contrary, the more 

 complete is their differentiation, the more complete also is inter- 

 their integration ; that is to say, the more unlike they ^^tion of 

 become, the more perfectly their functions are combined, £ m?nT 



r 2 



