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.” 
