LIFE ON THE EAETH. 215 



true in a restricted sense ; of employing infinite time 

 to integrate quantities which are subject to no law 

 of varying magnitude; and of assigning a resultant 

 to unknown and inconstant directions? Do we not 

 find the 'mutability of species' illustrated by ex- 

 amples of limited change, effected by the directing 

 agency of man ; and then what stands for an infer- 

 ence that unlimited changes have been effected or 

 are in progress by the undirected combination of 

 external conditions? Are we sure that varieties 

 which are given by nature in successive generations, 

 can be summed in one direction by the variable 

 preponderant of a number of concomitant variable 

 conditions of life? Can we remove 'natural selec- 

 tion' from the large synonymy of 'chance,' except 

 by giving to one of the variable conditions of which 

 it is the sum, direction, definite value or effect ? Is 

 it not the one acknowledged possession by every 

 species of an inherent tendency to propagate its 

 like? Would not the effect of this one constant 

 among any number of variables without law, be to 

 preserve the characters of the species for ever ? And 

 if 'natural selection' were regarded as giving direc- 

 tion to these variables, in combination with that 

 constant tendency, what would be the final result 

 but that which has always been recognized, viz. a 

 species varying within limits which are to be sought 



