6 THE BIOLOGICAL PROBLEM OF TO-DAY 



stitute the foremost task of biology. The prose- 

 cution of biological investigation will continuously 

 endow the theory of epigenesis with a fuller and 

 fuller meaning, but will never transform it into a 

 solution final in the sense of the theory of pre- 

 formation. 



It seems to me that the significance of Wolff's 

 doctrine lies in this : it rejected the purely formal 

 theory of preformation because actual observations 

 were against it. Thereby Wolft' freed research 

 from the straitened bonds of prejudice, and entered 

 the only possible path by which science can advance 

 -the path along which the biology of our century 

 has made so great advances. 



Biologists of to-day approach the problem of 

 organic development equipped with incomparably 

 greater knowledge and with more delicate methods 

 of research. But in our thoughts to-day, as we 

 discuss the essential nature of the process of organic 

 development and the mutual causal relations be- 

 tween rudiments and their products, the same con- 

 tradictory views are present, altered only as our 

 methods of expression have altered. 



In a striking fashion Roux 1 has contrasted the 

 opposing ideas inherent in our modern conception 

 of development, but yet identical with those which 

 formerly found expression in the theories of pre- 

 formation and epigenesis. 



c By the term " embryonic development," in its 



1 "VVilhelm Roux in Zcitsclirift fiir Pioloylc, vol. xxi. (1SS5) : 

 Zilr Ori^ntinnui iicJicr rinlai- Proll^m,- <I<T Embryondleii Ert1 iclcJc- 

 luny. 



