150 



trace in unbroken ascent the eYolution from species to 

 species, or from family to family. We see the 

 principle of variation at work in existing nature ; we 

 can trace the broad outline of an ascent from lower to 

 higher in the past — and this ascent in time in 

 wonderful harmony with the ordinal rank that pre- 

 vails among living forms j and as we know the 

 intimate dependence of life on physical conditions, 

 so we ascribe its variations and newer aspects mainly 

 to the influence of external forces. Nay, more, we 

 see the development of the whole vital plan, so 

 wonderfully analogous to the development of the 

 individual, that we cannot refuse to associate with the 

 evolution of the one the conditions which we know 

 are indispensable to the growth of the other. This, 

 however, is all, and as science has and can have no 

 other object than the establishment of truth, it is as 

 frank in admitting its defects as it is firm in main- 

 taining its demonstrations. In its attacks on the 

 citadel of the unknown it may recoU baffled and toil- 

 worn ; but " the failures of the past only prepare for 

 the triumphs of the future.'' 



In the meantime, then, however zealous some may 

 be in their advocacy of the development theory, it 

 must be regarded more in the Ught of an inference 

 than received as a scientific demonstration. Geology 

 has not yet discovered the connecting links, as it were, 



