Weismanris theory of Evolution (1891). 87 



the Metaphyta and Metazoa. At most it can have 

 been continuous only in the attenuated sense, that 

 however much and however often its hereditary 

 characters may have been modified by somatic 

 changes on the one hand or by changes in the 

 external conditions of life on the other, they can 

 never have been thus modified representatively, as 

 supposed by the theory of pangenesis. 



From which it follows that, while examining in 

 our last chapter Weismann's doctrine of the per- 

 petual continuity of germ-plasm, we have been 

 indirectly examining also his companion doctrine of 

 the unalterable stability of germ-plasm. Neverthe- 

 less, for the sake of doing justice to both these 

 doctrines, I have thought it desirable to examine 

 each on its own merits, without prejudice arising 

 from our criticism of the other. To such a separate 

 and independent examination of the doctrine of 

 unalterable stability we will, therefore, now proceed. 



As we have already and repeatedly seen, this 

 doctrine of the unalterable or absolute stability of 

 germ-plasm " since the first origin of sexual propaga- 

 tion" is a logically essential part of Weismann's 

 theory of evolution, or of his system of hypotheses 

 considered as a whole. It is so because upon this 

 doctrine depends his reference of individual variations 

 in the Metazoa to an ultimate origin in the Protozoa, 

 the significance of sexual reproduction in the theory 

 of natural selection, &c, &c. Therefore this doctrine 

 of the absolute stability of germ-plasm is enunciated 

 by Weismann, not merely for the purpose of meeting 

 any one class of facts, such as those of atavism 



