phesident's address. 21 



ileteruiinaiits of uiorpliological change are of llic .s.iiuo type ub the 

 structural alteration wrought in the dog's brain. 



The mnemic theory — at any rate that form of it held by Semon 

 and by myself — agrees with the current view, viz., that the nucleus 

 is the centre of development, or, in Semon's phraseology, that the 

 nucleus contains the engrams in which lies tlie secret of the ontogenetic 

 rhythm. But the mode of action of the mnemic nucleus is com- 

 pletely different from that of Weismann. He assumes that the nucleus 

 is disintegrated in the course of development by the dropping from it 

 of the determinants which regulate the manner of growth of successive 

 groups of cells. But if the potentiality of the germ nucleus depends on 

 the presence of engrams, if, in fact, its function is comparable to that of 

 a nerve-centre, its capacity is not diminished by action ; it does not cast 

 out engrams from its substance as Weismann's nucleus is assumed to 

 drop armies of determinants. The engrams are but cut deeper into the 

 records, and more closely bonded one with the next. The nucleus, con- 

 sidered as a machine, does not lose its component parts in the course 

 of use. We shall see later on that the nuclei of the whole body may, 

 on the mnemic theory, be believed to become alike. The fact that 

 the mnemic theoi-y allows the nucleus to retain its repeating or repro- 

 ductive or mnemic quality supplies the element of continuity. The 

 germ-cell divides and its daughter cells form the tissues of the embryo, 

 and in this process the original nucleus has given rise to a group of 

 nuclei ; these, however, have not lost their engrams, but retain the 

 potentiality of the parent nucleus. "We need not therefore postulate the 

 special form of continuity which is characteristic of Weismann's theory. 



We may say, therefore, that the mnemic hypothesis harmonises with 

 the facts of heredity and ontogeny. But the real difficulties remain to 

 be considered, and these, I confess, are of a terrifying magnitude. 



The first difficulty is the question how the changes arising in the soma 

 are, so to speak, telegraphed to the germ-cells. Hering allows that such 

 communication must at first seem highly mysterious.^ He then proceeds 

 to show how by the essential unity and yet extreme ramification of the 

 nervous system ' all parts of the body are so connected that what happens 

 in one echoes through the rest, so that from the disturbance occurring in 

 any part some notification, faint though it may be, is conveyed to the 

 most distant parts of the body.' 



A similar explanation is given by Nageli. He supposes that adaptive, 

 in contradistinction to organic, characters are profluced by external 

 causes ; and since these characters arc hereditary tliere must be com- 

 munication between the seat of adaptation and tlie germ-cells. Tliis 

 telegraphic effect is supposed to be effected by the network of idioplasm 

 which traverses the body, in the case of plants by the intercellular proto- 

 plasmic threads. 



' E. Hering in Ostwald's Klasmker der exakten. U'issenscliufte/i, No. 118, p.,14; 

 see also S. Butler's translation in Unconscious Memory, p. liy. 



