264 



characters might be contrasted as hlastogenic, because they include 

 all those characters in the body whicli have arisen from changes 

 in the germ. In this way we might prevent the possibility of a 

 misunderstanding. We maintain that the somcttogeiiic character 

 cannot be transmitted, or rather that those who assert that they 

 can be transmitted must furnish the requisite proofs. 



" The somatogenic characters not only include the effects of 

 mutilation, but the changes which follow from increased or dim- 

 inished performance of function, and those which are directly 

 due to nutrition and any of the other external influences which 

 act upon the body. 



" Among the hlastogenic characters we include not only all the 

 changes produced by natural selection operating upon variations 

 in the germ, but all other characters which result from this latter 

 cause.'' 



For example, a man may either be born with some malforma- 

 tion of one of his fingers or he may acquire such malformation 

 or mutilation as the result of accident or disease. Now in the 

 former case, wiien the malformation is congenital, it is extremely 

 probable that the peculiarity will be transmitted to his children, 

 while in the case where the man has himself acquired the de- 

 formity, it is, according to Weismann, certain that there will be 

 no such transmission. 



It is quite true that both medical men and biologists have long 

 been aware of the remarkable tendency tliat exists for the in- 

 heritance of congenital deformity, but it has been at the same 

 time generally assumed that acquired characters might also be 

 regarded as similarly hereditable, though with less certainty and 

 to a less extent. The difference thus being considered to be one 

 of degree merely. Weismann makes it one of kind, and states 

 it to be a physiological impossibility that acquired characters, as 

 defined by him, can be transmitted under any circumstances. 



He declares that the evidence put forward by other biologists 

 in favour of the opposite view, which he discusses at considerable 

 length in one of his essays, is either unreliable or inconclusive. 

 On this same question much discussion has recently taken place 

 in the pages of Nature between some of the most distinguished 

 biologists of the day ; indeed, it still continues with unabated 

 vigour. 



We are now in a position to resume consideration of Weis- 

 mann's central theory of heredity, and, recapitulating the sub- 

 stance of what has gone before, we have seen that the body of 

 the multicellular organism is composed of two entirely different 

 kinds of cells — germ-cells and somatic-cells — the former being 

 concerned solely with reproduction and the latter with the build- 



