306 DEVELOPMENT AND PURPOSE CHAP. 



activity dovetail in with one another and maintain an 

 equilibrium among an ever-moving set of forces. Whether 

 through a subtle mechanism or otherwise, the result is 

 reached that the several parts do not act independently but 

 in mutual relation. Mechanical < indifference ' is replaced 

 by organic < consensus.' Bringing the two opposed terms 

 down to their last analysis, so far as it is as yet before us, 

 we may say that two parts a and b of a whole are mechani- 

 cally related when the operation of each is uniformly deter- 

 mined by its own structure alone ; they are organically 

 related when the operation of a is itself affected by the 

 effect which it has upon b and vice versa. 



We shall have to return upon this definition very shortly 

 and to ask not only whether it is satisfactory in itself, but 

 whether it serves adequately to distinguish a living organ- 

 ism from a machine. It will be well, first, to remark most 

 briefly that the consensus which we have recognised affects 

 not only the daily and hourly working of the organism, 

 but its structural growth. Just as between two functions 

 so between two structures, modification is met with modifi- 

 cation. Within the limits of organic adaptability altera- 

 tions of conditions are met by a responsive growth of 

 structure which, whether with or without some general 

 modification of type, enables the life process to be main- 

 tained. In the first place, the normal development of the 

 entire organism, and of every part of it considered inter- 

 nally, is a correlated development. Starting, as it does, 

 with the division of a single cell, apparently through the 

 development of certain centres and radiant lines of tension, 

 the very first stage presents us with two cells determined 

 in size, character, contents and position by the mutual 

 relations, the relative tendencies of different portions of 

 the substance of the mother-cell to hold together or to split. 

 Each stage of growth involves essentially similar processes 

 of cell division, and thus the gradual differentiation of 

 parts out of a relatively simple and homogeneous structure 

 is a process in which, take it where we will, each new 

 element is a differentiation involving its complement. But 

 further, the lines of differentiation are not absolutely pre- 

 determined for each individual embryo. On the contrary, 



