104 ON HEREDITY. 



possible that the effects of these influences may be more specialized ; 

 that is to say, they may act only upon certain parts of the germ- 

 cells. But this is indeed very different from believing- that the 

 changes of the organism which result from external stimuli can 

 be transmitted to the germ-calls and will re-develope in the next 

 generation at the same time as that at which they arose in the 

 parent, and in the same part of the organism. 



^ We have an obvious means by which the inheritance of all 

 transmitted peculiarities takes place, in the continuity of the 

 substance of the germ-cells, or germ-plasm. If, as I believe, the 

 substance of the germ-cells, the germ-plasm, has remained in per- 

 petual continuity from the first origin of life, and if the germ- 

 plasm and the substance of the body, the somatoplasm, have always 

 occupied different spheres, and if changes in the latter only arise 

 when they have been preceded by corresponding changes in the 

 former, then we can, up to a certain point, understand the principle 



^of heredity; or, at any rate, we can conceive that the human 

 mind may at some time be capable of understanding it. We may 

 at least maintain that it has been rendered intelligible, for we 

 can thus trace heredity back to growth ; we can thus look upon 

 reproduction as an overgrowth of the individual, and can thus 

 distinguish between a succession of species and a succession of 

 individuals, because in the latter succession the germ-plasm remains 

 similar, while in the succession of the former it becomes different. 

 Thus individuals, as they arise, are always assuming new and more 

 complex forms, until the interval between the simple unicellular 

 protozoon and the most complex of all organisms man himself- 

 is bridged over. 



I have not been able to throw light upon all sides of the question 

 which we are here discussing. There are still some essential points 

 which I must leave for the present ; and, furthermore, I am not 

 yet in a position to explain satisfactorily all the details which 

 arise at every step of the argument. But it appeared to me to be 

 necessary to state this weighty and fundamental question, and to 

 formulate it concisely and definitely ; for only in this way will it 

 be possible to arrive at a true and lasting solution of the problem. 



' We must however be clear on this point that the understanding 

 of the phenomena of heredity is only possible on the fundamental 



L supposition of the continuity of the germ-plasm. The value of 



