THE ELEMENTS OF ORGANIC EVOLUTION. 



99 



by the most laborious research ; and while we may pre- 

 dict that conclusive evidence of its existence will be 

 found in morphology, it is safe to add that the fortunate 

 discoverer will be a physiologist. 



" Chief among the unknown factors are the relations 

 between the various stages of development and the en- 

 vironment." 



Professor Osborn concludes this discussion with the 

 belief that " progressive inheritance is rather a process 

 of substitution of certain characters and potentialities 

 than the actual elimination implied by Weismann. " My 

 last word is," he says, " that we are entering the thresh- 

 old of the evolution problem instead of standing within 

 the portals. The harder tasks lie before us, not behind 

 us, and their solution will carry us well into the twenti- 

 eth century." 



