EQUILIBRATION. 515 



rangements, must be such as will meet all the forces acting 

 on the aggregate, by equivalent antagonistic forces. What is 

 the implication in the case of organic aggregates; the equi- 

 librium of which is a moving one? We have seen that the 

 maintenance of such a moving equilibrium, requires the 

 habitual genesis of internal forces corresponding in number, 

 directions, and amounts to the external incident forces as 

 many inner functions, single or combined, as there are single 

 or combined outer actions to be met. But functions are the 

 correlatives of organs; amounts of functions are, other 

 things equal, the correlatives of sizes of organs; and combi- 

 nations of functions the correlatives of connections of or- 

 gans. Hence the structural complexity accompanying 

 functional equilibration, is definable as one in which there 

 are as many specialized parts as are capable, separately and 

 jointly, of counteracting the separate and joint forces amid 

 which the organism exists. And this is the limit of organic 

 heterogeneity; to which man has approached more nearly 

 than any other creature. 



Groups of organisms display this universal tendency to- 

 wards a balance very obviously. In 85, every species of 

 plant and animal was shown to be perpetually undergoing a 

 rhythmical variation in number now from abundance of 

 food and absence of enemies rising above its average; and 

 then by a consequent scarcity of food and abundance of ene- 

 mies being depressed below its average. And here we have 

 to observe that there is thus maintained an equilibrium be- 

 tween the sum of those forces which result in the increase of 

 each race, and the sum of those forces which result in its de- 

 crease. Either limit of variation is a point at which the one 

 set of forces, before in excess of the other, is counterbalanced 

 by it. And amid these oscillations produced by their con- 

 flict, lies that average number of the species at which its 

 expansive tendency is in equilibrium with surrounding re- 

 pressive tendencies. Nor can it be questioned that this bal- 

 ancing of the preservative and destructive forces which 



