338 THE INDUCTIONS OF BIOLOGY. 



extremely active changes which go on during the early 

 stages of evolution, imply an immense excess of the mole- 

 cukr forces over those antagonist forces which the aggregate 

 exercises on the molecules. While this excess continues, it 

 is expended in growth, development, and function: expendi- 

 ture for any of these purposes being proof that part of the 

 force constituting molecular tensions remains unbalanced. 

 Eventually, however, this excess diminishes. Either, as in 

 organisms which do not expend much energy, decrease of 

 assimilation leads to its decline; or, as in organisms which 

 expend much energy, it is counterbalanced by the rapidly- 

 increasing reactions of the aggregate (§46). The cessation 

 of growth when followed, as in some organisms, by death, 

 implies the arrival at an equilibrium between the molecular 

 forces and those forces which the aggregate opposes to them. 

 When, as in other organisms, growth ends in the establish- 

 ment of a moving equilibrium, there is implied such a 

 decreased preponderance of the molecular forces, as leaves 

 no surplus beyond that which is used up in functions. The 

 declining functional activity characteristic of advancing life, 

 expresses a further decline in this surplus. And when 

 all vital movements come to an end, the implication is 

 that the actions of the units on the aggregate and the 

 reactions of the aggregate on the units are completely 

 balanced. Hence, while a state of rapid growth indi- 



cates such a play of forces among the units of an aggregate 

 as will produce active re-distribution, the diminution and 

 arrest of growth shows that the units have fallen into such 

 relative positions that re-distribution is no longer so facile. 

 When, therefore, we see that gamogenesis recurs only when 

 growth is decreasing, or has come to an end, we must say 

 that it recurs only when the organic units are approximating 

 to equilibrium — only when their mutual restraints prevent 

 them from readily changing their arrangements in obedience 

 to incident forces. 



That units of like forms can be built up into a more stable 



