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.

    162/522 (page 132)
    132 the germ-plasm. that is, regeneration in two directions—cannot take place in the higher animals. If, then, regeneration depends on the distribution of supple¬ mentary determinants to certain cells, which occurs whenever it is necessary or possible, the process must be primarily traceable in the case of the Metazoa to the doubling of the ids in a certain ontogenetic stage. And since a division and doubling of the idants takes place in every mitotic nuclear division, this hypothesis is supported by actual fact, even although we are still far from being acquainted even with the general details of the processes of growth and doubling of the ids and determinants, not to mention the systematic transference of such inactive determinants to definite cells and series of cells. Here again, however, Nature will have caused an advance from the simple to the more complex ; and it therefore follows that, just as complicated organisms could only arise in the course of innumerable series of generations and species, so also the complex apparatus for regeneration in the tail or limb of a newt could not have been developed suddenly, but must have arisen in consequence of similar modifications in innumerable ancestors. It might be possible to picture to one's self approximately the series of modifications which the apparatus for regeneration has gradually undergone, beginning at the lowest multicellular forms, and passing upwards to those animals in which the power of regeneration is the most highly developed and complex. I shall not, however, attempt to do so. At some future date it may perhaps be found that differences occur as regards the number of ids contained in the cells of those which have, and in those which have not, a marked capacity for regeneration : it will not be worth while to trace in detail the courses which the development of the power of regeneration has taken, vmtil our knowledge of the idioplasm is sufficiently complete to furnish a basis for the theory in fact. 4. Regeneration in Plants. The process which may be described as regeneration in the case of the lower plants—the algse, fungi, and mosses—will be treated of in greater detail subsequently. In this place, I merely wish to point out that true regeneration only occurs in a very slight degree in all the higher plants which are regarded as cormophytes or plant-stocks. If a piece is cut out of a