FOR many years a link in the chain of Samuel Butler’s biological works has been missing. “Unconscious Memory” was originally published thirty years ago, but for fully half that period it has been out of print, owing to the destruction of a large number of the unbound sheets in a fire at the premises of the printers some years ago. The present reprint comes, I think, at a peculiarly fortunate moment, since the attention of the general public has of late been drawn to Butler’s biological theories in a marked manner by several distinguished men of science, notably by Dr. Francis Darwin, who, in his presidential address to the British Association in 1908, quoted from the translation of Hering’s address on “Memory as a Universal Function of Original Matter,” which Butler incorporated into “Unconscious Memory,” and spoke in the highest terms of Butler himself. It is not necessary for me to do more than refer to the changed attitude of scientific authorities with regard to Butler and his theories, since Professor Marcus Hartog has most kindly consented to contribute an introduction to the present edition of “Unconscious Memory,” summarising Butler’s views upon biology, and defining his position in the world of science. A word must be said as to the controversy between Butler and Darwin, with which Chapter IV is concerned. I have been told that in reissuing the book at all I am committing a grievous error of taste, that the world is no longer interested in these “old, unhappy far-off things and battles long ago,” and that Butler himself, by refraining from republishing “Unconscious Memory,” tacitly admitted that he wished the controversy to be consigned to oblivion. This last suggestion, at any rate, has no foundation in fact. Butler desired nothing less than that his vindication of himself against what he considered unfair treatment should be forgotten. He would have republished “Unconscious Memory” himself, had not the latter years of his life been devoted to all-engrossing work in other fields. In issuing the present edition I am fulfilling a wish that he expressed to me shortly before his death. R. A. STREATFEILD. _April_, 1910. Introduction By Marcus Hartog, M.A., D.Sc., F.L.S., F.R.H.S. IN reviewing Samuel Butler’s works, “Unconscious Memory” gives us an invaluable lead; for it tells us (Chaps. II, III) how the author came to write the Book of the Machines in “Erewhon” (1872), with its foreshadowing of the later theory, “Life and Habit,” (1878), “Evolution, Old and New” (1879), as well as “Unconscious Memory” (1880) itself. His fourth book on biological theory was “Luck? or Cunning?” (1887). {0a}