PHYSIOLOGICAL INTEGRATION IN ANIMALS. 373 



to make it a line of diminished resistance ; then, in propor- 

 tion as any parts become more physiologically integrated by 

 the establishment of this channel for the easy transmission 

 of molecular motion between them, they may become more 

 physiologically differentiated. The contrast between their 

 molecular motions leads to the line of discharge ; the line of 

 discharge, once formed, permits a greater contrast of their 

 molecular motions to arise ; thereupon the quantities of 

 molecular motion transferred to restore equilibrium, being 

 increased, the channel of transfer is made more permeable : 

 and its further permeability, so caused, renders possible a still 

 more marked unlikeness of action between the parts. Thus 

 the differentiation and the integration progress hand in hand 

 as before. How the same principle holds through- 



out the higher stages of nervous development, can be seen 

 only still more vaguely. Nevertheless, it is comprehensible 

 that as functions become further divided, there will arise the 

 need for sub-connexions along which there may take place 

 secondary equilibrations subordinate to the main ones. It is 

 manifest, too, that whereas the differentiation of functions 

 proceeds, not necessarily by division into two, but often by 

 division into several, and usually in such ways as not to leave 

 any two functions that are just complementary to one another, 

 the restorations of equilibrium cannot be so simple as 

 above supposed. And especially when we bear in mind that 

 many differentiated functions, as those of the senses, cannot 

 be held complementary to any other functions in particular ; 

 it becomes manifest that the equilibrations that have to be 

 made in an organism of much heterogeneity, are extremely 

 complex, and do not take place between each organ and some 

 other, but between each organ and all the others. The pecu- 

 liarity of the molecular motion propagated from each organ, 

 has to be neutralized by some counter-peculiarity in the 

 average of the molecular motions with which it is brought 

 into relation. All the variously-modified molecular motions 

 from the various parts, must have their pluses and minuses 



