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 seerned 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 preformation, 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 
