THE BIOLOGICAL PROBLEM OF TO-DA Y 



complexity, an actual increase of complexity. 

 Evolution, on the other hand, would imply the 

 mere becoming visible of pre - existing latent 

 differentiation. Clearly, according to these general 

 definitions, occurrences which outwardly exhibit 

 epigenesis may be in reality partial or complete 

 evolution. In fact, the deepest consideration leads 

 us again to the original question : Is embryonic 

 development epigenesis or evolution ? Is it the 

 new formation of complexity, or is it the becoming 

 visible of complexity previously invisible to us ?' 



Thus, in our own days, after the controversy has 

 been at rest for long, biologists are assembled in 

 opposing groups, one under the standard of epi- 

 genesis, another under that of preformation. 



Weismann 1 leads the van for preformation ; for 

 the last ten years he has occupied himself with the 

 theoretical discussion of the questions set forth 

 above ; and now, in a recent treatise, The Germ- 

 plasm, he has combined his views, already many 

 times modified, in a coherent theory. Now he ex- 

 plains candidly that he has been driven to the 

 view that epigenetic development does not exist. 

 * In the first chapter of my book,' he remarks, ' will 

 be found an actual proof of the reality of evolution, 

 a proof so simple and obvious that I can scarcely 

 understand to-day how it could have escaped my 

 notice so long' (Germplasm, p. 14). Elsewhere he 

 writes : c I believe that I have established that 



1 See Weismann's Collected Essays, Clarendon Press (2nd edit. ), 

 vol. i. , 1891, vol. ii., 1892 ; and Weismann's Germplasm, Walter 

 Scott's Contemporary Science Series-, 1893. The references in this 

 translation are to the latter volume. 



