54 Varietäten, Descendenz, Hybriden. 



in the modern sense depends upon epigenetic changes or addi- 

 tions to the ontogenetic rhythm. This view is in direct antagonism 

 to the widely held view that ontogeny is only to be altered by a 

 fundamental upset — by alteration in the germ-cell. 



On the epigenetic theory new species must arise by the germ- 

 cells being the deposit, par excellence, of the associated engrams 

 of former Stimuli and as these are only to be slowly built up by 

 repetition it foUows that 1) successive generations must be mnemi- 

 cally connected and 2) the germ-cells must be constantly receptive 

 of Stimulation experienced by the whole soma. This is the real wor- 

 king of the Inheritance of Acquired Characters. 



Weismann's Theory: Any theory of evolution must account 

 for 1) the fact of ontogeny, being the more or less predetermined 

 development of the ovum and 2) the fact of heredity, being the 

 approximation of the developed form to that of the parent. 



Between the mnemic theory and Weismann's theory of evolu- 

 tion there can only be war to the knife. Darwin holds that the 

 Isolation of germ-plasm which so smoothly explains heredity is not 

 borne out by a direct study of development nor by the facts of 

 regeneration. It is agreed that there are no facts to decide critically 

 between these theories: it is always logically possible to attribute 

 apparent inheritance of acquired characters to Variation of germ- 

 plasm; but the acceptance of the mnemic view of inheritance demands 

 somatic inheritance. 



The Mnemic Theory: The application of this theory to explain 

 ontogeny presents no difificulties but this is not so in explaining heredity. 



In ontogeny the determining factors will not be hypothetical 

 'determinants' as on Weismann's theory but the associated engrams 

 of acquired habit of which we all have experience. These the author 

 locates in the nucleus which would thus shed nothing in ontogenesis 

 but each somatic nucleus would retain its records in the complete 

 way that the most striking phenomena of regeneration demand. 



For heredity it must be assumed that the germ-cell has recor- 

 ded in it the engrams of previous somatic experience. With 

 Hering and Nägeli, Darwin hypothecates that each local expe- 

 rience spreads faintly over the whole body producing engrams in 

 every somatic nucleus and also in the germ nucleus which on this 

 view demands no provision of special continuity. 



The building- up of efficient engrams in germ cells by repetition 

 must of course be very slow and is not easy to explain as a me- 

 chanism. Constant influencing of germ-cells by nervous Communi- 

 cations seems quite inadequate unless qualitative differences of nerve 

 Impulses are accepted. Rignano simplifies the work of the germ- 

 nucleus by analogies drawn from electric accumulators. He holds 

 that the local disturbance on Stimulation travels to the germ nucleus 

 and affects it in a precisely similar way to the local nuclei. When 

 the cellular descendents of the germ-cell reach that stage of onto- 

 geny at which the record was originally made then a sort of inhe- 

 rited Stimulus is set free from nuclei as from an accumulator. 



Darwin contributes a Suggestion that the existence of pain and 

 pleasure may really simplify the problem of inheritance. One may 

 assume that only the main phenomena of movement and morphology 

 are transmitted purely by inheritance and that the details of their 

 correct application are acquired by the individual by trial and error 

 upon the fringe of the danger zone, failure to react correctly to 

 this being met by the penalty of pain or death. 



