Introduction 7 



is able in its turn to include a number greater still. So 

 soon as a hypothesis pushes a bit nearer to the beleaguered 

 fortress, so to speak, and indicates new lines for study, 

 observation and research, one must admit that it has ful- 

 filled its purpose. And this applies to our view of the new 

 biogenetic hypothesis which we here submit to the judg- 

 ment of biologists and of positive philosophers in general. 



We have believed it expedient to follow in the exposi- 

 tion of this theory the order in which it was conceived 

 and built up, and so the first chapter describes briefly the 

 inductive way in which the author, starting out from the 

 fundamental biogenetic law, was led to the conception of 

 his hypothesis. In the three following chapters are col- 

 lected and arranged as concisely as possible the principal, 

 different, biogenetic facts which, quite independently of 

 the ever controverted question of the inheritance of 

 acquired characters, serve best to set forth and define the 

 new hypothesis and which, since they find in it their most 

 complete explanation, confirm it again directly or in- 

 directly in a deductive way. 



After having then undertaken in the fifth chapter a 

 brief examination of the question of the inheritance or 

 the non-inheritance of acquired characters which until 

 then we had laid entirely aside, we pass in the sixth 

 chapter to the critical exposition of the principal biogene- 

 tic theories which are current at present. And we do this 

 not only with the object of showing their inadequacy to 

 explain the mechanism of inheritance, but rather in 

 order that the perception of the reason of this inadequacy 

 may aid us in discovering the necessary and sufficient con- 

 ditions required in any theory which seeks to explain this 

 inheritance. After that we go on again in the seventh 

 chapter with the examination of our hypothesis whose 



