September 25, 1908] 



SCIENCE 



391 



is merely a specialized somatic cell and has 

 the essential qualities' of the soma. With 

 regard to ontogeny, I have already pointed 

 out that Weismann does not seem to ex- 

 plain its automatic character. 



THE MNEMIC THEORY 



If the mnemic theory is compared with 

 Weismann 's views it is clear that it is 

 strong precisely where these are weakest 

 —namely, in giving a coherent theory of 

 the rhythm of development. It also bears 

 comparison with all theories in which the 

 conception of determinants occurs. Why 

 should we make elaborate theories of hypo- 

 thetical determinants to account for the 

 potentialities lying hidden in the germ- 

 cell, and neglect the only determinants of 

 whose existence we have positive knowl- 

 edge (though we do not know their pre- 

 cise nature) ? We know positively that 

 by making a dog sit up and then giving 

 him a biscuit we build up something in his 

 brain in consequence of which a biscuit 

 becomes the stimulus to the act of sitting. 

 The mnemic theory assumes that the de- 

 terminants of morphological change are of 

 the same type as 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 center of development, or, 

 in Semon 's phraseology, that the nucleus 

 contains the engrams in which lies the 

 secret of the ontogenetic rhythm. But the 

 mode of action of the mnemic nucleus is 

 completely different from that of Weis- 

 mann. He assumes that the nucleus is dis- 

 integrated 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 po- 

 tentiality of the germ nucleus depends on 

 the presence of engrams, if, in fact, its 

 function is comparable to that of a nerve- 



center, its capacity is not diminished by 

 action; it does not cast out engrams from 

 its substance as Weismann 's nucleus is as- 

 sumed to drop armies of determinants. 

 The engrams are but cut deeper into the 

 records, and more closely bonded one with 

 the next. The nucleus, considered 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 be- 

 come alike. The fact that the mnemic the- 

 ory allows the nucleus to retain its repeat- 

 ing or reproductive or mnemic quality sup- 

 plies 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 poten- 

 tiality of the parent nucleus. We need not, 

 therefore, postulate the special foz'm of con- 

 tinuity which is characteristic of Weis- 

 mann 's theory. 



We may say, therefore, that the mnemic 

 hypothesis harmonizes with the facts of 

 heredity and ontogeny. But the real difS- 

 culties 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. Her- 

 ing 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 con- 

 nected that what happens in one echoes 

 through the rest, so that from the disturb- 

 ance occurring in any part some notifica- 

 tion, faint though it may be, is conveyed to 

 the most distant parts of the body." 



A similar explanation is given by Nageli. 



'° E. Hering in Ostwald's Klassiker der exakten 

 Wissenschaften, No. 148, p. 14; see also S. But- 

 ler's translation in " Unconscious Memory," p. 119. 



