102 THE LESSON OF EVOLUTION 



to grow, no equilibrium can be arrived at between 

 the whole and its parts. Under these conditions an 

 undifferentiated portion of the aggregate will be able 

 to arrange itself into the structure peculiar to the 

 species, and will so arrange itself, if freed from 

 controlling force, and placed in fit conditions of 

 nutrition and temperature. But let growth be 

 checked and development approach completion, let 

 the units of the aggregate be severally exposed to an 

 almost constant distribution of forces, and they must 

 begin to equilibrate themselves-. Arranged, as they 

 will gradually be, into comparatively stable attitudes 

 in relation to one another, their mobility will 

 diminish, and groups of them, partially or wholly 

 detached, will no longer readily rearrange themselves 

 into the specific form." And further on (p. 519) he 

 says, " Every change is towards a balance of forces ; 

 and of necessity can never cease until a balance of 

 forces is reached." And (p. 522) " This equilibra- 

 tion between the functions of an organism and the 

 actions in its environment may be either direct or 

 indirect. The new incident force may either imme- 

 diately call forth some counteracting force, and its 

 concomitant structural change ; or it may be 

 eventually balanced by some otherwise produced 

 change of function and structure. These two pro- 

 cesses of equilibration are quite distinct and must be 

 separately dealt with." However, indirect equili- 

 bration is explained as identical with the survival 

 of the fittest, and therefore relates to the preserva- 

 tion, not to the origination of variations. 



Darwin's hypothesis of Pangenesis, given at the 



