PREFACE XUl 



very hypothesis from which it derives its name is untenable. 

 There is now scarcely any doubt that the entire conception 

 of the production of the ' gemmules ' by the body-cells, their 

 separation from the latter, and their ' circulation,' is in real- 

 ity wholly imaginary. In this regard I am still quite as much 

 opposed to Darwin's views as formerly, for I beheve that 

 all parts of the body do not contribute to produce a germ 

 from which the new individual arises, but that, on the con- 

 trary, the offspring owes its origin to a peculiar substance 

 of extremely complicated structure, viz., the * germ-plasm.' 

 This substance can never be formed anew ; it can only 

 grow, multiply, and be transmitted from one generation to 

 another. My theory might therefore well be denominated 

 *" bias to -gene sis ' — or origin from a germ-plasm, in contradis- 

 tinction to Darwin's theory of ^pangenesis ' — or origin from 

 all parts of the body. 



My doubts as to the validity of Darwin's theory were for a \, 

 long time not confined to this point alone : the assumption | 

 of the existence oi p7'eformed constituents of all parts of the 

 body seemed to me far too easy a solution of the difficulty, \ 

 besides entailing an impossibility in the shape of an abso- | 

 lutely inconceivable aggregation of primary constituents. I ^ 

 therefore endeavoured to see if it were not possible to 

 imagine that the germ-plasm, though of complex structure, 

 was not composed of such an immense number of particles, 

 and that its further complication arose subsequently in the 

 course of development. In other words, what I sought was 

 a substance from which the whole organism might arise by 

 epigefiesis, and not by evolution* After repeated attempts, 



* The theory of * evolution ' or * preformation ' of the early physiolo- 

 gists supposed that all parts of the fully-formed animal or plant were 

 present, in a minute form, in the germ. The rival theory of * epigenesis ' 



