Introduction rs 
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 
