The Biological Problem of To-day: Preformation Or Epigenesis? / The Basis of a Theory of Organic Development

by Oscar Hertwig

[8] The following treatises contain criticisms of Weismann's theories: W. Haacke, Gestaltung und Vererbung; Leipzig, 1893; Herbert Spencer, articles in Contemporary Review (1893-94); Romanes, An Examination of Weismannism; Longmans, 1893.

[9] Notwithstanding the objections raised by Bergh, Verworn, and Haacke, I abide by the supposition that the nucleus of reproductive cells contains the hereditary mass or germinal material. My reasons may be found in my text-book on The Cell (English edit., p. 274). Briefly they are: 1. The equivalence of the male and female hereditary masses. 2. The equal distribution of the growing nuclear mass of the primary egg-cell among the daughter-cells that, arising from it, build up the organism. 3. The preservation of a constancy of bulk of the hereditary mass when fertilization occurs. 4. The isotropism of protoplasm. Following Pflüger, I mean by isotropism that the protoplasm of the egg does not contain local areas for the formation of different organs; but that, according to the conditions, any part of the protoplasm may be employed in the formation of any organ. Isotropism is merely the negation of His' doctrine of the presence of local areas for definite organs, and without losing its meaning, is compatible with the fact that many eggs have their poles different, and that others have a bilateral symmetry which determines the plane of the first division. 5. The fact that the first stages of many embryonic developments consist in the multiplication of the nuclear material and its distribution in the yolk, following which the yolk-mass cleaves into cells.

[10] English edition, p. 32.

[11] English edition, p. 34.

[12] In this section upon heteromorphosis I rely upon the following treatises, which have appeared recently. Loeb, Untersuchungen zur physiologischen Morphologie der Thiere. Organbildung und Wachsthum. Heft, 1 and 2 (1891-1892). H. de Vries, Intracellulare Pangenesis (1889). H. Driesch, Entwicklungsmechamische Studien, i.-vi.; Zeitschrift f. wissenschaft, Zool., vol. liii.-lv. The same, Zur Theorie der thierischen Formbildung. Biol. Centralblatt, vol. xiii., 1893. Chabry, Contribution à l'embryologie normale et tératologique des Ascidies simples. Jour. de l'Anat. et de Physiol. (1887). Wilson, Amphioxus and the Mosaic Theory. Journal of Morph. (1893). See also Anatomischer Anzeiger (1892).

[13] Roux tried to give experimental evidence in favour of his mosaic theory in a treatise On the Artificial Productions of Half-Embryos by the Destruction of one of the first two Cleavage-Cells, and on the Reconstruction of the Lost Parts. Virchow's Archiv., vol. cxiv., 1888. Roux defends his mosaic theory against Driesch and myself in (1) Ueber das entwicklungsmechanische Vermögen jeder der beiden ersten Furchungszellen des Eies. Verhandl. der Anat. Gesellsch. der 6^ten Versamml. in Wien, 1892. (2) Ueber Mosaikarbeit und neuere Entwicklungshypothesen. Anatomische Hefte von Merkel und Bonnet (1893). Also in Biol. Centralblatt (1893); in the Anatom. Anzeiger (1893), and in the treatise Die Methoden zur Erzeugung halber Froschembryonen und zum Nachweis der Beziehung der ersten Furchungsebenen des Froscheies zur Medianebene des Embryo. Anatom. Anzeiger. (1894); Nos. 8 and 9.

If, as would appear from the last treatise, Roux would avoid being reckoned with evolutionists, he must abandon his mosaic theory, and this he has not done. I think in the present essay, on theoretical and experimental grounds I have shown the untenability of Roux's mosaic theory.

[14] The terms vertical and horizontal refer to the vertical axis of the egg, which passes through the animal and vegetative poles.—Translator's note.

[15] Further details concerning these experiments may be found in Hertwig, Ueber den Werth der ersten Furchungszellen für die Organbildung des Embryo. Experimentelle Studien am Froschund Tritonei. Archiv. für Mikrosk. Anatomie, vol. xlii., 1893, p. 710; Plate xli.; Figs. 1, 2, 27.

[16] For the facts in this section I rely in particular upon the writings of Vöchting, Bert, Ollier, Trembley, Landois, Ponfick, and others: