6 Introduction 



devised to give any explanation whatever, even an un- 

 satisfactory one, of the mechanism of that inheritance. 

 Yet the author never lost sight of the fact that natural 

 selection in no way sufficed to explain phylogenetic evolu- 

 tion completely, and he was always convinced that 

 non-inheritance was irreconcilable with the fundamental 

 biogenetic law that ontogeny is only a recapitulation of 

 phylogeny. This law, whose remote and immediate 

 consequences constantly stimulated the reflection of the 

 author, has finally led him in a purely inductive way to 

 the new biogenetic hypothesis about to be presented. 



It seemed to the author that he ought to devote a 

 special effort to the elaboration and exposition of this 

 hypothesis, for he saw from the outset that it promised 

 an explanation not only for the inheritance of acquired 

 characters but also, and quite independently, for a whole 

 series of fundamental biological phenomena, and how it 

 afforded an outlet from the blind alley into which onto- 

 genetic biology seems to have run: for while some facts 

 lead us to reject epigenesis as it is commonly understood, 

 others force us to reject pre formation, and similarly 

 while a whole series of reasons force us to hold as 

 inadmissable a homogeneous germinal substance or a sub- 

 stance only chemically heterogeneous, another whole 

 series of reasons obliges us to hold no less inadmissable a 

 germinal substance constituted by the germs of the 

 preformists. 



The author knows well that he must not entertain any 

 oversanguine expectations. In the position of biological 

 science today we can deal only with preliminary hypoth- 

 eses, of which each gives way to its successor and each, 

 taking in a greater number of phenomena than its pred- 

 ecessor prepares the way for a later hypothesis which 



