Weismann’s Theory Cannot Explain Biogenetic Law 221 
responding to the last ontogenetic stage, must be also 
capable of transforming in the most different ways the 
determinants of the other stages. According to that, 
each phylogenetic stage would have its own ontogeny, 
which would differ completely even in the first stages of 
development from the ontogeneses of the preceding 
phyletic stages. 
And there is no more reason for the supposition that 
the only way in which the determinants corresponding to 
the last ontogenetic stage could undergo modification 
must be by “obtaining a greater power of growth, aug- 
menting consequently in number, differentiating each in 
a new fashion, and adding thus at the end of the old 
ontogeny one or more generations of cells.”1° For 
these determinants could perhaps undergo any merely 
qualitative variation whatever without first augmenting 
in number, that is to say could become differentiated at 
once in a new way so that the part determined by them 
should at once take on a form different from the old one 
without needing first to pass through its preceding 
phylogenetic state. 
We need just to recall again the example which we 
have already cited above, furnished by one of the most 
characteristic manifestations of the fundamental bio- 
genetic law, namely ontogenetic involution, in order to 
demonstrate in the clearest way the absolute inability of 
Weismann’s theory, to account for that law. For accord- 
ing to that theory one would understand for instance that 
the tail of the ancestor of the tadpole, or that the limbs of 
the ancestor of the existing serpent may have become con- 
stantly shorter in the course of phylogeny by virtue of 
26°Weismann: Ibid. P. 110. 
