PREFACE. 



THIS book consists of Lectures which were given by me 

 during the winter terms of 1905 to 1907 at the Humboldt 

 Academy and the Urania in Berlin. 



My object in delivering them was to show that it is no 

 longer possible, having regard to the advances of modern research, 

 to find complete satisfaction in being an out-and-out believer 

 in the Darwinian or Lamarckian or any other theory. 



Each of these doctrines has rendered important service in 

 promoting our knowledge, but the marks of their limitations have 

 of recent years become increasingly distinct. 



The factors which the different doctrines assume to be at 

 work in the genesis and evolution of the organic world are, 

 however, not exclusive, for the Theory of Selection, the Doctrine 

 of Adaptation and of Use and Non-use, and finally de Vries' 

 Theory of Mutations, offer each for a certain section of organic 

 evolution a sufficient and satisfactory explanation. 



That, on the other hand, a vast field of vital processes remains 

 still hidden and unexplained only dogmatic prejudice will venture 

 to deny. 



If I have succeeded in conveying to a wider circle this 

 conception of conflicting theories, and if I have further succeeded 

 in showing that "incomprehensible" does not mean " impossible 

 to comprehend," my object in publishing these Lectures in 

 book form has been attained. 



CURT THESING. 



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