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. 



