164 



HABIT AND INTELLIGENCE. 



[chap. 



Develop- 

 ment of 

 functions 

 by diflfer- 

 eutiation. 



I hope I have now said enough to make intelligible the 

 statement at the beginning of this chapter, that vital 

 functions are developed one out of the other by gradual 

 differentiation. Formative, motor, and sensory functions 

 are no doubt too fundamentally distinct to be produced by 

 differentiation the one from the other.^ But within each 

 of these three groups there is so perfect a gradation 

 between the various kinds, or rather the various grades, 

 of functions, that it is easily seen how one may be de- 

 veloped out of the other. In the vegetative or formative 

 series, the first and simplest functions are the chemical 

 ones. Above these are the structural functions, the lowest 

 and simplest of which is the formation of cells. Now cells 

 are formed by a chemical differentiation between the con- 

 stituents of the inside and the outside of the cell ; so that 

 the chemical function here passes into the structural one. 

 And a gradation is manifestly possible from the formation 

 of the simplest cellular tissue to that of the most complex 

 organ. In the motor series, the gradation is decided : it 

 is impossible to say where the one grade ends and the 

 other begins. The same is equally true of the sensory, 

 though perhaps less obvious : but I defer this part of my 

 subject tdl I come to treat formally of ISIind. 



In the next chapter I shall have to state the peculiar 

 laws of life on which the possibility of this gradation 

 depends. 



1 See Note B (p. 166). 



