Contrasting the generally received view with his own, Professor Weismann says that according to the first of these "the organism produces germ-cells afresh again and again, and that it produces them entirely from its own substance." While by the second "the germ-cells are no longer looked upon as the product of the parent's body, at least as far as their essential part--the specific germ- plasm--is concerned; they are rather considered as something which is to be placed in contrast with the tout ensemble of the cells which make up the parent's body, and the germ-cells of succeeding generations stand in a similar relation to one another as a series of generations of unicellular organisms arising by a continued process of cell-division." {274a} On another page he writes:-- "I believe that heredity depends upon the fact that a small portion of the effective substance of the germ, the germ-plasm, remains unchanged during the development of the ovum into an organism, and that this part of the germ-plasm serves as a foundation from which the germ-cells of the new organism are produced. There is, therefore, continuity of the germ-plasm from one generation to another. One might represent the germ-plasm by the metaphor of a long creeping root-stock from which plants arise at intervals, these latter representing the individuals of successive generations." {274b} Mr. Wallace, who does not appear to have read Professor Weismann's essays themselves, but whose remarks are, no doubt, ultimately derived from the sequel to the passage just quoted from page 266 of Professor Weismann's book, contends that the impossibility of the transmission of acquired characters follows as a logical result from Professor Weismann's theory, inasmuch as the molecular structure of the germ-plasm that will go to form any succeeding generation is already predetermined within the still unformed embryo of its predecessor; "and Weismann," continues Mr. Wallace, "holds that there are no facts which really prove that acquired characters can be inherited, although their inheritance has, by most writers, been considered so probable as hardly to stand in need of direct proof." {275} Professor Weismann, in passages too numerous to quote, shows that he recognizes this necessity, and acknowledges that the non- transmission of acquired characters "forms the foundation of the views" set forth in his book, p. 291. Professor Ray Lankester does not commit himself absolutely to this view, but lends it support by saying (Nature, December 12, 1889): "It is hardly necessary to say that it has never yet been shown experimentally that _anything_ acquired by one generation is transmitted to the next (putting aside diseases)."