Weismann s theory of Heredity (1891). 75 



are enormously complex and our ignorance unusually 

 profound — is always precarious. Lastly, in the fifth 

 place, Weismann has now himself abandoned this 

 argument. For in one of his later essays he says : — 



Those instances of early separation of sexual from somatic 

 cells, upon which I have often insisted as indicating the con- 

 tinuity of the germ-plasm, do not now appear to be of such 

 conclusive importance as at the time when we were not sure 

 about the localization of the plasm in the nuclei. In the great 

 majority of cases the germ-cells are not separated at the 

 beginning of embryonic development, but only in some of the 

 later stages. ... It therefore follows that cases of early separa- 

 tion of the germ-cells afford no proof of a direct persistence of 

 the parent germ-cells in those of the offspring. 



The last line of direct evidence, or that derived 

 from the alleged non-variability of parthenogenetic 

 organisms, is, as Professor Vines has shown, opposed 

 to fact. Therefore, in his later writings, Weismann 

 has abandoned this line of evidence also. 



Upon the whole, then, we must conclude with regard 

 to the fundamental postulate of perpetual continuity, 

 that there is actually no evidence of a direct kind in 

 its favour. And, as Weismann's arguments of an 

 indirect kind are dealt with in Appendix I, it remains 

 only to state such evidence per contra as, to the best 

 of my judgement, appears valid. 



The fundamental proposition which we have been 

 considering, and to the further consideration of which 

 we have now to proceed, is, in effect, that germ-plasm 

 differs from stirp in having been perpetually restricted 

 to a "sphere" of its own, "since the first origin of 

 life!' Criticism, therefore, must be directed to show 

 that the " sphere " in question has not been proved 



