My present task is twofold; it has both a positive and a negative side. First, I have to examine the arguments recently alleged in favour of the theory of preformation, testing them to reveal their inherent weaknesses, and to controvert their fallacies. As Weismann unquestionably is the chief of those who have advocated preformation, and has made a closed system of it again, it is necessary for me to take special notice of his conception as it is set forth in The Germplasm. Although I am no friend of polemic, the case demands it. For the decision of a question so momentous as the relative scopes of evolution and epigenesis in embryology must have an important bearing on the future of biology, upon its aim and the method of research.
But criticism of Weismann's hypothesis is not to be an end in itself; I am more anxious to show the lines upon which, as I think, the real meaning of the process of organic development will come to be learned. In a second section, therefore, I shall explain my own views in greater detail, and, as I hope, place them on a firmer foundation than formerly was possible.
FOOTNOTES:
[1] Wilhelm Roux in Zeitschrift für Biologie, vol. xxi. (1885): Zür Orientirung ueber einige Probleme der Embryonalen Entwicklung.
[2] See Weismann's Collected Essays, Clarendon Press (2nd edit.), vol. i., 1891, vol. ii., 1892; and Weismann's Germplasm, Walter Scott's Contemporary Science Series, 1893. The references in this translation are to the latter volume.
[3] The Germplasm, p. 137.
[4] Ibid., p. 138.
[5] The ideas expressed in this book may be found, in an elementary condition, in various publications of my own, and written in conjunction with my brother, Richard Hertwig: Oscar and Richard Hertwig, Die Actinien; Jena, 1879 (pp. 203-217). Oscar Hertwig, Das Problem der Befruchtung und der Isotropie des Eies, eine Theorie der Vererbung; Jena, 1884. Oscar Hertwig, Vergleich der Ei- und Samenbildung bei Nematoden, Arch. f. Mikrosk. Anatomie, vol. xxxvi., 1890, pp. 77-128. Oscar Hertwig, Urmund und Spina bifida, Arch. f. Mikrosk. Anatomie, vol. xxxix., 1892, pp. 476-492. Oscar Hertwig, Aeltere und neuere Entwicklungstheorien; Berlin, 1892. Oscar Hertwig, The Cell: Sonnenschein; London, 1895. Oscar Hertwig, Ueber den Werth der ersten Furchungszellen für die Organbildung des Embryo, Arch. f. Mikrosk. Anatomie, vol. xlii., 1893. The chief other writers to whom I refer are: Herbert Spencer, Principles of Biology. Darwin, Pangenesis, a Provisional Hypothesis (in Variation of Plants and Animals under Domestication). Haeckel, Die Perigenesis der Plastidule. Weismann, loc. cit., p. 8. Naegeli, Mechanisch-physiologische Theorie der Abstammungslehre; München, 1884. Strasburger, Neue Untersuchungen ueber den Befruchtungsvorgang bei den Phanerogamen als Grundlage für eine Theorie der Zeugung, 1884. H. de Vries, Intracellulare Pangenesis. W. His, Unsere Körperform und das physiologische Problem ihrer Entstehung, 1874. W. Roux, loc. cit., p. 6. Driesch, loc. cit., p. 48.
[6] An English translation, The Cell, was published by Swan Sonnenschein and Co. in 1895.