“MAN,” writes the learned and genial Carl Ernst von Baer, “considers himself just as necessarily in the centre of his mental horizon as of his mathematical one.” When, in the closing hours of the last day of the nineteenth• century, I wrote this citation in the original German, as the opening words of the preface of the first of a series of memoirs upon the history of the germ-cells, I little reckoned that the controversy regarding their story, which was the final link in the general principle of an antithetic alternation of generations, would be carried on around the side-issue— the special case in von Helmholtz’s sense—of the origin, nature, and scientific treatment of cancer. All of these are concerns of embryology, for they are problems of reproduction, growth, and the stereo-chemical processes of life. In the discussion of a similar problem of embryology—that of parthenogenesis (paedogenesis) or virgin reproduction in fly- maggots (Cecidomya)—von Baer used the above words. His account of this discovery of Wagner’s has its special interest in connection with the present work.
Carl Ernst von Baer writes:* “ that at first the dis.
* Baer, can Ernst von: “Uber Prof. Nic. Wagner’s Entdeckung von Larven, die sich fortpflanzen, Herrn Ganin’s verwandte und ergânzende Beobachtungen und über die Paedogenesis überhaupt,” in Melanges Biologiques, v., 1865, pp. 203-308; loc. cit., pp. 241-243.