GENESIS, HEREDITY, AND VARIATION. 275 



extremely active changes which, go on during the early 

 Btages 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 oi 

 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; tho 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 stable 



