The germ-plasm : a theory of heredity / [A. Weismann] ; translated by W. Newton Parker and Harriet Rönnfeldt.

  • Weismann, August, 1834-1914.
Date:
1893
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The germ-plasm : a theory of heredity / [A. Weismann] ; translated by W. Newton Parker and Harriet Rönnfeldt. Source: Wellcome Collection.

    53/522 (page 23)
    INTRODUCTION. 23 that by far the larger part of the egg-cell does not consist of hereditary substance, and that the latter only constitutes a small portion even of the sperm-cell. From his observations on the egg of the star-fish, Oscar Hertwig had suspected that the essential part of the process of fertilisation consists in the union of the nuclei of the egg- and sperm-cells, and as it is now known that the hereditary substance is undoubtedly contained in the nucleus, this view has, in this respect at least, proved to be the right one. It is true that the nucleus of the male cell is always surrounded by a cell-body, and that Strasburger's opinion to the contrary is incorrect. We now know, through the researches of Guignard, that even in Phanerogams a small cell-body surrounds the nucleus, and that a special structure, the ' centrosome,'—which is absolutely essential for the commence¬ ment of development,—is contained within it. This structure will be treated of in further detail presently, but I must here lay stress upon my view, that the '' cenirosome'' with its ^sphere of attraction^ cannot in any case be the hereditary substance, and that it is merely aii apparatus for the division of ^he cell and nucleus. Both in animals and plants, however, essentially the same substance is contained in the nucleus both of the sperm-cell and egg-cell:—this is the hereditary substance of the species. There can now be no longer any doubt that the view which has been held for years by Strasburger and myself is the correct one, according to which the nuclei of the male and those of the female germ-cells are essentially similar., i.e.., in any given species they contain the same specific hereditary substance. The splendid and important investigations carried out by Auerbach, Biitschli, Flemming, and many others, on the detailed processes of nuclear division in general, and those dealing more particularly with the fertilisation of the egg in Ascaris by van Beneden, Boveri, and others, have given us the means of ascertaining more definitely what portion of the nucleus is the substance on which heredity depends. As already remarked, this substance corresponds to the ' chromosomes,' those rod-like, looped, or granular bodies which are contained in the nucleus, and which become deeply stained by colouring matters. As soon as it had been undoubtedly proved that the nucleus, and not the body of the cell, must contain the hereditary sub¬ stance, the conclusion \vas drawn that neither the membrane of