Weismauii s theory of Heredity (1891). 49 



will be devoted to examining Weismann's theory of 

 heredity, while the ensuing chapter will be concerned 

 with his sequent theory of evolution. 



Again, Weismann's theory of heredity stands on 

 his fundamental postulate — the continuity of germ- 

 plasm; and also on a fact well recognized by all other 

 theories of heredity, which he calls the stability of 

 germ-plasm. But his sequent theory of evolution 

 stands not only on this fundamental postulate, and on 

 this well-recognized fact ; it requires for its logical 

 basis two further postulates — viz., that germ-plasm 

 has been perpetually continuous " since the first origin 

 of life," and unalterably stable " since the first origin 

 of sexual propagation." That these things are so. 

 a very few words will be sufficient to prove. 



Any theory of heredity which supposes the material 

 of heredity to occupy a more or less separate " sphere " 

 of its own, is not obliged further to suppose that this 

 material has always been thus isolated, or even that 

 it is now invariably so. There have been one or two 

 such theories prior to Weismann's, and they were 

 founded on the well-known fact of congenital characters 

 being at any rate much more heritable than are 

 acquired characters. But it has not been needful for 

 these theories to assume that the "continuity" thus 

 postulated has been. perpetually unbroken. Even if it 

 has been frequently to some extent interrupted, all 

 the facts of heredity could be equally well comprised 

 under such theories — and this even if it be supposed 

 that acquired characters are but rarely, or never, 

 transmitted to progeny. For, in as far as the con- 

 tinuity may have been interrupted, it does not follow 

 that the acquired characters (body-changes), which by 



E 



