GENESIS, HEREDITY, AND VARIATION. 275 



cjstremely active changes which go on during the early 

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

 cular 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 embodied in molecular tensions, remains unbalanced. 

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

 organisms which do not expend much force, decrease of assi- 

 milation leads to its decline ; or, as in organisms which ex- 

 pend much force, it is counterbalanced by the rapidly-increas- 

 ing re-actions of the aggregate (§ 46). The cessation o( 

 growth, when followed, as in some organisms, by death, im- 

 plies 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 de- 

 creased preponderance of the molecular forces, as leaves no 

 surplus beyond that which is used up in functions. The de- 

 clining 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 re- 

 actions of the aggregate on the units, are completely bal- 

 anced. 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 ; tha 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 approxima- 

 ting to equilibrium — only when their mutual restraints pre- 

 vent them from readily changing their arrangements in obe- 

 dience to incident forces. 



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



