Weismann's Theory Cannot Explain Bio gene tic 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." 169 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 



"'Weismann: Ibid. P. no. 



