100 BIOLOGICAL LECTURES. 



Heredity is also to be made much clearer by a series of experi- 

 ments directed to palingenic variation, in order to ascertain 

 how far the revival of an ancient environment arouses latent 

 hereditary forces. The experiments already well advanced by 

 Cunningham, Agassiz, and Poulton indicate that progressive 

 inheritance is rather a process of substitution of certain charac- 

 ters and potentialities than the actual elimination implied by 

 Weismann. 



My last word is, that we are entering the threshold of the 

 Evolution problem, instead of standing within the portals. 

 The hardest tasks lie before us, not behind us, and their solu- 

 tion will carry us well into the twentieth century. 



