The Germ-plasm : a theory of heredity / by August Weismann ; translated by W. Newton Parker and Harriet Ronnfeldt.

  • Weismann, August, 1834-1914.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: The Germ-plasm : a theory of heredity / by August Weismann ; translated by W. Newton Parker and Harriet Ronnfeldt. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    481/510 (page 457)
    one half remained inactive, and was then either passed on as inactive ' blastogenic' germ-plasm, or else became divided up in the course of ontogeny into groups, which were passed separately to the same region, viz., that of the bud. In all cases in which the power of budding was permanently retained by the species, the occurrence of this process of doubling of the germ-plasm seems to have persisted through the ontogenetic stages from an early period ; for we find that the individuals arising by gemmation very frequently vary in- dependently of one another, and often even to a great extent. But independent variation from the germ onwards implies the existence of special determinants in the 'blastogenic' germ-plasm. Medusae could never have been produced from polypes by budding if independently variable determinants of the buds had not been present in the germ of the fertilised ovum. We therefore assume that iwo kinds of germ-plasm exist in those species in which alternation of generations occurs, both of which are present in the egg-cell as well as in the bud, though only one of them is active at a time and controls ontogeny, while the other remains inactive. The alternating activity of these two germ-plasms causes the alternation of generations. The formation of germ-cells is brought about by the occur- rence of similar processes in the idioplasm to those which cause gemmation. One part of the germ-plasm contained in the ferti- lised egg-cell remains inactive and ' unalterable,'—that is, it does not immediately become disintegrated into groups, but is'passed on m the form of accessory idioplasm to certain series of cells m ontogeny, and thus reaches the parts in which germ-cells are to be formed. Thus the whole of the parental germ-plasm with all Its determinants, forms the foundation of the germ-cells which will give rise to the next generation, and the extremely accurate and detailed transmission of parental characters to the offspring is thereby rendered comprehensible. In multicellular plants and animals, the germ-plasm becomes more complex in consequence of sexual reproduction, in which process the ids of two different individuals, the parents, are accumulated in the fertilised egg-cell every time amphimixis oc- curs This has caused the occurrence of the ' reducing division ' which accompanies the formation of male and female germ-cells' and results in the number of ids and idants being reduced to