250 Theories Treating of Inheritance 
the constant precision in the repetition even of the most 
minute peculiarities, stipulate fundamentally an individual 
ontogenetic factor, which is directive and at the same 
time co-ordinative, acting at each moment of develop- 
ment throughout the entire organism even to the smallest 
single parts of it. But ontogenetic theories like those of 
Herbst or His take a stand diametrically opposed to this. 
It is also almost superfluous to remark that they cannot 
give the least account of the repetition of phylogeny by 
ontogeny, and still less of the inheritance of acquired 
characters. 
For the latter, as we can well assert without needing to 
fear that we get too far from the truth, requires ab- 
solutely the condition, certainly not sufficient, yet at least 
necessary, that just this ontogenetic factor of individual 
nature should act everywhere and incessantly and also 
that it should not give up the control of development 
even for a moment, so that it may thus be in a position 
to experience in itself each variation even the smallest 
appearing in the organism in consequence of any new 
functional adaptation. But the theories of Herbst and 
His, and all others like them, which have recourse only 
to the principle of fructifying causality, rest upon the 
conception that the successive influences would always 
be left to themselves by their respective special causes, 
as soon as they had once been produced and launched, 
so to speak, into development, to produce in their turn 
new influences. 
Therefore these theories necessarily exclude any 
inheritance of acquired characters. But if this latter 
actually exists they become, as we have said, quite 
untenable from this point of view also. 
