president's address. — SECTION D. 265 



the external stimulus is transformed into this vital energy. A deposit 

 of a specific substance takes place in the nuclei of the modified cells, 

 and the energy current leads to a like deposit in the cells of a central 

 zone of development. This central zone is, in higher animals, the less 

 differentiated portion of the central nervous system. The central zone 

 influences in its turn the germ plasm as we know it, giving it a new 

 potentiality. When in development that stage of dyjiamic equilibrium 

 is reached in which the parent organism stood at the time of the modi- 

 fication, then the new potentiality of the germ cell gains expression. 

 This it does by setting up in a reverse direction the energy current under 

 whose influence it was formed. The result of this is the development 

 of the new cells in accordance with the modified form. Rignano's 

 theory is one that must excite our admiration on account of its ingenuity 

 and the completeness of its machinery, even though we should think 

 that the specific substance and the accommodation of this in the germ 

 plasm need demonstration, and should find difficulty with regard to 

 the means of transformation of the original stimulus into vital energy. 



With Rignano's ingenious theory may be compared the theory 

 sketched in the following passage in Cunningham's Revie w of Super- 

 Organic Evolution, by Enrique Lluria (Science Progress, Vol. V,, 

 1910-11, p. 169). Lluria's conception of the course of human evolution 

 involves the assumption of the transmission of somatic, expecially 

 cerebral modifications ; but he adopts the theory that this transmission 

 is effected by means of the nervous system, evidently in ignorance of 

 the recent discoveries which tend to show that the connexion 

 between the gonads and the soma is chemical and not 

 nervous. In support of his view he quotes a Manual of Pathol- 

 ogy, the authors of which, Hillemand and Petrucci, state that " the 

 heredity of acquired characteristics is a cerebro-medullar reflex action 

 upon the germinating cells, the impressions received by the reflex 

 centres of the grey substance of the brain being transmitted to the 

 genital centre of the medulla and finally to the ovoblasts and spermato- 

 blasts by the nerve fillets, which starting from this centre are distributed 

 in the testicles and ovaries." 



If the review of Lluria's theory is an adequate one, and there is 

 no reason to doubt it, the view is one that need not concern us greatly. 

 We want something that applies to all organisms, plant or animal ; 

 and to all stages of the organism, not least to those stages that precede 

 the development of the central nervous system when there is a nervous 

 system to develop. 



In an address such as this there is not time to give an account of 

 the various forms of mnemic theory. Many of those present are familiar 

 with the views set forth by Hering, Semon, Butler, Haeckel, Dendy, 

 and Francis Darwin. 



