In my theory two assumptions of totally contrasting nature are made: I assume a germplasm of high and specific organisation, and I assume that this is transformed into the adult product by epigenetic agencies. To a certain extent, therefore, I reconcile the opposition between evolution and epigenesis, these opponents so prominent last century. But my theory does not pretend to explain all the many problems involved in the course of organic development. In this respect it differs from Weismann's doctrine of determinants, as that is a closed system, finding within itself a formal explanation of all development. So far it seems to me an abandonment of explanation rather than an explanation; for it explains by signs and tokens that elude verification and experiment, and that cannot encounter concrete investigation. His explanation is no more than a description, in other words, of the visible events of development. To be more than this, it would be necessary to explain how in each case the biophores and determinants and ancestral plasms are constituted, and how they are arranged in the architecture of the germplasm so as to produce the development of the egg-cell in this or that fashion. It must, at the least, offer such possibilities as the structural formulæ of chemists offer. But in the present stage of our knowledge Weismann's method is unpromising; it merely transfers to an invisible region the solution of a problem that we are trying to solve, at least partially, by investigation of visible characters; and in the invisible region it is impossible to apply the methods of science. So, by its very nature, it is barren to investigation, as there is no means by which investigation may put it to the proof. In this respect it is like its predecessor, the theory of preformation of the eighteenth century. FOOTNOTES: [17] The second section contains references to the following treatises: C. V. NAEGELI: _Mechanisch-physiologische Theorie der Abstammungslehre_ (1884). HERTWIG, OSCAR: _Lehrbuch der Entwicklungsgeschichte des Menschen und der Wirbelthiere_; 4th edit. SACHS: _Lectures on Plant Physiology_; English edition, Clarendon Press. VOECHTING: _Ueber die Theilbarkeit im Pflanzenreich und die Wirkung innerer und äusserer Kräfte auf Organbildung an Pflanzentheilen._ _Pflüger's Archiv._, vol. xv., 1877. Ibid.: _Ueber Organbildung im Pflanzenreich_, 1, 2; Bonn, 1878, 1884. GOEBEL: _Beiträge zur Morphologie und Physiologie des Blattes._ _Bot. Zeit._, 1880. PFLÜGER: _Die teleologische Mechanik der lebendigen Natur_; Bonn, 1877. MAUPAS: _Sur le déterminisme de la sexualité chez l'Hydatina senta._ _Comptes rendus des séances de l'Académie des Sciences_; Paris, 1891. WEISMANN: _Die Allmacht der Naturzüchtung. Eine Erwiderung an Herbert Spencer_; Jena, 1893. HERBERT SPENCER: _A Rejoinder to Professor Weismann._ _Contemporary Review_, 1893. Ibid.: _Die Unzulänglichkeit der 'Natürlichen Zuchtwahl.'_ _Biol. Centralblatt_, vol. xiv., No. 6.