II.] ON HEREDITY. I05 



the germ itself. I will not enter into this subject at any length 

 on the present occasion, for I have already expressed my 

 opinion upon it\ 



I believe however that they can be referred to the various 

 external influences to which the germ is exposed before the 

 commencement of embryonic development. Hence w^e may 

 fairly attribute to the adult organism influences which deter- 

 mine the phyletic development of its descendants. For the 

 germ-cells are contained in the organism, and the external in- 

 fluences which affect them are intimately connected with the 

 state of the organism in which they lie hid. If it be well 

 nourished, the germ-cells will have abundant nutriment ; and, 

 conversely, if it be weak and sickly, the germ-cells will be 

 arrested in their growth. It is even 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 trans- 

 mitted to the germ-cells 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-celts, or germ-plasm. If, as I believe, the 

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

 perpetual 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 correspond- 

 ing 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 over- 

 growth of the individual, and can thus distinguish between a 

 succession of species and a succession of individuals, because 



* Consult 'Studicn zur Descendenzthcorie, IV. (Jbcr die mechanische 

 Auffassung dcr Natur,' p. 303, etc. Translated and edited by Professor 

 Meldola; see * Studies in the Theory of Descent,' p. 677, etc. 



