Weismanris theory of Evolution (1891). 89 



of the whole matter — the place where germ-plasm is 

 supposed to be unchangeable is not the place where 

 it is most likely to be so, but the place where it is 

 least likely. For germ-plasm as it occurs in the germ- 

 cells of multicellular organisms must have a constitu- 

 tion greatly more complex even than that which it has 

 in unicellular organisms — seeing that in the former 

 case, and by hypothesis, it bears a living record of the 

 whole phylogeny of the Metaphyta and Metazoa in 

 all their innumerable branchings. And not only so, 

 but when germ-plasm occurs in germ-cells it becomes 

 exposed to much greater vicissitudes : its environment 

 has become vastly more complex, as well as greatly 

 more liable to change with the changing conditions of 

 life of the many mutable species in which it resides, 

 and on the individual somas of which it now depends 

 for its nourishment. So that, altogether, we have here 

 on merely a priori grounds about as strong a case 

 against this doctrine of absolute stability as it is well 

 conceivable that on merely a priori grounds a case 

 can be. 



Turning next to arguments a posteriori, let us begin 

 by considering those which Weismann has adduced in 

 support of the doctrine. 



First, he alleges that there is a total absence of 

 variability on the part of all organisms which have 

 been produced parthenogenetically, or from unfer- 

 tilized ova. We may look in vain, he says, for any 

 individual differences on the part of any multi- 

 cellular organisms, which have been brought into ex- 

 istence independently of the blending of germ-plasms 

 in a previous act of sexual union. Now, unques- 

 tionably, if this statement could be corroborated by 



