The principles of heredity with some applications / by G. Archdall Reid.

  • Reid, G. Archdall (George Archdall O'Brien), Sir, 1860-1929.
Date:
1905
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Licence: In copyright

Credit: The principles of heredity with some applications / by G. Archdall Reid. Source: Wellcome Collection.

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    ofif minute “gemmules” which are then dispersed through the body where they multiply, and whence they are collected into the germ-cells; each of the latter thus being packets of gemmules which later develop, each gemmule in its proper place, into the somatic cells of the offspring. The other set of theories supposes that the germ-plasm is not derived from the cells of the soma, but directly from pre-existing germ- plasm. Thus Weismann in his theory of the “ Continuity of the Germ-plasm ” supposes that, when an individual develops from a germ-cell, the germ-plasm contained in that cell divides into two portions, from one of which, after undergoing great changes and growth, is derived his soma, and from the other his germ-cells. According to the first set of theories the germ-plasm is formed anew in every individual from materials derived from his tissues. According to the second it is not formed anew, but is simply a reserved portion of the germ-plasm from which his own soma was derived. .,15. None of these theories are capable of direct proof or disproof. The hereditary substance, the germ-plasm, has been identified with a high degree of probability with the chromatin of the nuclei. When cells multiply the chromatin of the parent cells is distributed to the nuclei of the daughter cells. The continuity of the germ-plasm is therefore practic- ally certain. But it is quite beyond the powers of our microscopes to inform us whether the germ-plasm does, or does not, receive additional germinal elements from the soma. We know that it must’receive non-living nutritive material, but that is not the same thing. The question, therefore, can be tested, only in an indirect way. If the first set of theories be true, if the soma does contribute germinal elements, and the various structures of the offspring are derived in part at least from the corresponding structures of the parent, then it follows that the child must tend to reproduce the acquirements as well as the inborn traits of the parent. On the other hand, if the structures of the child are not derived from the corresponding structures of the parent, then the inheritance of acquired characters is evidently highly improbable. 16. Formerly all the world believed in the transmission of acquired characters. The discovery that offspring take origin from single cells (generally fertilized ova) did not affect this belief at first. Darwin’s theory of “ Pangenesis,” for example, expressed the popular faith in scientific terms. He tried to explain how acquired characters are transmitted by supposing that the hereditary substance in the germ-cells is derived
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