VARIABILITY 11 



unjustifiable on the basis of the facts offered to us by the 

 organic world now living, and which is contradicted by the 

 general conception of the gradual development and perfection 

 of organic differentiation. But Weismann compares the 

 increase of the continually unchanged germ -plasm of the 

 multicellular organism with the reproduction of the 

 unicellular; in the latter also the same substance grows 

 continually, and new individuals arise only by its division 

 from time to time. The germ -plasm of the multicellular 

 organisms is to correspond therefore with the whole body 

 of the unicellular. Weismann does not deny that the 

 unicellular beings change in consequence of the direct 

 influence of external agencies ; on the contrary, he ascribes 

 to them explicitly this property. From this inheritable 

 individual diversity once produced he derives " that of the 

 Metazoa and Metaphyta, 1 in that this diversity, through 

 sexual reproduction which has in the meantime become 

 general, is preserved for ever, increased and ever produced 

 in new combinations." Thus, according to Weismann, the 

 difference between the unicellular organism and the germ- 

 plasm of the multicellular is a fundamental one for the 

 former other laws hold good than for the latter. 



But against Weismann's conception of the importance 

 of the germ-plasm in heredity are to be set the following 

 facts. 



It is known that even highly organised animals and plants 

 have the power of multiplying, by simple division in the case 

 of the former, by cuttings in that of the latter. The new 

 complete individual produced by this method has the same 

 characters as the animal or plant produced at another time 

 from a germ-cell a proof that the substance possessing the 

 property of heredity is not confined to the germ-plasm, and 



1 I.e. of the multicellular animals and plants. 

 2 Cf. V. v. Ebner, op. cit. 



