Note 110 — Chapter V · THE THEORY OF EVOLUTION AND THE DEVELOPMENT OF MORALITY.
Reading edition
It would seem that the transmission of mental qualities only takes place in the form of modified physical structure (cf. G. H. Lewes, Problems of Life and Mind, 1st series, i. 164). But, if we regard it as established that every mental change has a structural modification corresponding to it, the possibility of mental evolution and inheritance presents no new difficulty.