From the PRELIMINARY REMARKS. THE ADDRESS on Germinal Selection which Weismann delivered at the Leyden Congress of Zoologists having appeared in the Religion of Science series in an English translation, it seems fitting that the American and English public should also be made acquainted with the paper which I read three days later at the same Congress on the same subject, viz., definitely directed evolution - to explain which Weismann's theory of germinal selection was propounded. I did not speak in the general session of the International Congress of Zoologists, but in a special session only, and for this reason, if for no other, the contents of my paper have as yet become little known. Furthermore, my opponent has since published his lecture in separate pamphlet form (Jena, 1896; Eng. trans, in No. 19 of the Religion of Science Library, Chicago, 1896), and not without substantial alterations. Again, whilst the speculations upon which Weismann's germinal selection rests, have been made public in numerous short separate publications, which were as a rule immediately translated into English, my views, which are at diametrical variance with the aforesaid speculations, repose upon an unwieldy mass of facts, not easily accessible to the intelligent public at large. One only of my works has been translated into English, namely, my book on Die Enistehung der Arten auf Grund von Vererbung erworbener Eigenschaften nach den Gesetzen organischen Wachsens, I., Jena, 1888, under the altered title of Organic Evolution, Macmillan, London, 1889. In this book I opposed, and was in fact the first to oppose, the main tenets of the Weismannian hypothesis of germ-plasm, and I have had the satisfaction of seeing that the numerous arguments which support this hypothesis have from year to year been modified in my favor. Whilst, however, Weismann has never ceased altering his hypotheses, he has yet refused to abandon certain fundamental tenets of the same, as his denial of the heredity of acquired characters, his advocacy of chance in the production of variations, and the exclusive dominancy of utility show. He has thus, the more he has altered his views, plunged himself the more inextricably into untenable contradictions, the most exemplary of which is his germinal selection. But germinal selection is nothing else than an attempt to render innocuous, or at least to force into conformity with his theory, the facts established during the last twenty years by myself and my pupils, according to which the modification of organisms takes place not accidentally but in a few perfectly determinate directions. Like facts have also been established in America by Prof. Alpheus Hyatt with reference to the transformation of Ammonites....