220 Inheritance of Acquired Characters 
overmastering power, it will not leave behind any trace 
in the individual and certainly none in the species. 
Thus the inheritance of acquired characters, thanks 
to these two facts that the embryo is usually withdrawn 
from the influence of the environment, and that or- 
ganisms undergoing development are elastic and not 
plastic, shows itself to be completely capable of account- 
ing for the fundamental biogenetic law. Whatever in it 
could seem marvelous and enigmatic finds its natural so- 
ultion and the law itself becomes an immediate and neces- 
sary consequence of this inheritance. 
What on the contrary is the explanation which Weis- 
mann is able to give for this law? He thinks to explain 
it merely by the following laconic words: 
“The biogenetic law rests upon this, that phylogenetic 
development is accomplished partly by the addition of 
new ontogenetic stages at the end of ontogeny. In order 
that this latter may be attained, the preceding terminal 
stages must each time be run through again.” 1° 
But in this Weismann leaves just the most important 
part of the question out of consideration. Why can 
phylogenetic development take place only by the addition 
of new ontogenetic stages at the end of ontogeny? 
According to Weismann’s theory, there is no reason 
whatever why one should believe the determinants cor- 
responding to the last ontogenetic stage to be the only 
ones to undergo modifications, for one cannot forget that 
according to this theory each cell of each ontogenetic 
stage must have its own determinants.1® The same 
causes of differences in the nutrition or any other thing, 
which are capable of modifying the determinants cor- 
**™Weismann: Das Keimplasma. P. 110. 
***Weismann: Ibid. e. g. P. 97, 100, 232—233, 596. 
