198 HOLISM AND EVOLUTION chap. 



Mutation as the usual method of creative Evolution, we 

 now come back to the earlier Germ-cell theory of Weismann, 

 who initiated it and through it the second phase of Dar- 

 winism, and thus became, and still remains, the second most 

 important figure in the history of Darwinism. His great 

 and essential service consisted in this, that he found the 

 real source of Evolution in the inner factor of Variation, 

 and that he traced this factor to its seat in the germ-cells 

 of the organism. Not the outward mechanical struggle and 

 clash of organisms, but the penetralia of their deeply hidden 

 and sheltered germ-cells were the mysterious, spontaneous, 

 independent and original source of all organic development 

 and of the origin of species. Of course this theory became 

 possible only by reason of the rapid advance in the knowl- 

 edge of the cells, and especially of the part they play in 

 reproduction. But on the basis of that new knowledge the 

 theory became quite simple and indeed inevitable. The 

 body-cells of advanced organisms have no part or lot 

 in reproduction, and the seat of all organic variations 

 must therefore be looked for in the reproductive cells 

 of the parents. All organic progress was thus traced 

 back to the inmost nature of the organism itself, and 

 not to the environment or any mere external factor. 

 This is the essential truth in the hypothesis of Weismann, 

 and this constitutes his real and lasting contribution to 

 the theory of Evolution. The mysterious Variation which 

 forms the inner factor of Evolution has its seat and source 

 in the fructified ovum or germ-cell from which the new life 

 begins. There and nowhere else take place the great play 

 and inter-play of forces, tendencies and influences which 

 shape the destinies of life in organic development. This is 

 not the whole story, but it is important; it is indeed 

 fundamental. 



Weismann drew a sharp distinction between the individual 

 and the race, between the body-cells which constitute the 

 one and the germ-cells which are the carriers of the other. 

 According to him the race or species is continued unbroken 

 in the substance of the germ-cells, which flow on as a con- 



