1908. Tht British Association in Dubtin. 213 



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 mneniic 

 theor}' assumes that the determinants of morphological 

 change are of the same type as the structural alteration 

 wrought in the dog's brain. 



"The nucleus is the centre of development; in Semon's 

 phraseolog}' the nucleus contains the engrams in which lies 

 the secret of ontogenetic rhythm. But . . its function is 

 comparable to that of a nerve-centre ; it does not cast out 

 engrams, as Weismann's nucleus is assumed to drop armies 

 of determinants. . . The nuclei of the whole body may be 

 believed to become alike. The mnemic hypothesis harmon- 

 ises with the facts of heredity and ontogeny. But the 

 difficulties, . . I confess, are of a terrifying magnitude. . . 

 How are the changes arising in the soma telegraphed to the 

 nerve-cells ? . . In plants the flow must be conceived (accord- 

 ing to Semon) as travelling by intercellular plasmic threads, 

 but in animals primarily b}^ nerve trunks. . . To me it seems 

 conceivable that such telegraphy is possible. But I shall 

 hardly wonder if a majority of my hearers decide that the 

 available evidence in its favour is both weak and fantastic. 

 Nor can I wonder that . . the existence of somatic inheritance 

 is denied for v/ant of evidence. But . . it seems to me 

 certain that in development we have an actual insiance of 

 habit. If this is so, somatic inheritance must be a vera 

 caicsa. 



" The great engine of natural selection is taunted nowadays, 

 as it was fift}- years ago, with being merely a negative power. 

 The mnemic hypothesis of evolution makes the positive value 

 of natural selection more obvious. If evolution is a process 

 of drilling organisms into habits, the elimination of those that 

 cannot learn is an integral part of the process. . . It is 

 sureh' a positive gain to the harmon}' of the universe that 

 the discordant strings should break. . . ." 



The address was delivered in a quiet, }-et impressive, style, 

 not closely read, and with such judicious omissions from the 

 printed copy as to keep it within an hour's limit. Unfortun- 

 ately, the speaker's voice did not reach the farther parts of the 



