Volume 1

Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation.

  • Shipley A. E. (Arthur Everett), Sir, 1861-1927.
Date:
1891-1892
Catalogue details

Licence: Public Domain Mark

Credit: Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation. Source: Wellcome Collection.

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

    197/502 (page 179)
    1 IV.] FOUNDATION OF A THEORY OF HEREDITY. I 79 which must be given up in the other cases; although such advantage might consist in assisting the development of the fertilized ovum and not in any increase of the true fertilizing substance. At the present time we are indeed disposed to recognize this advantage in still more unimportant matters, but at that time the ascertained facts did not justify us in the assertion that fertilization is a mere fusion of nuclei, and M. Nussbaum ^ quite correctly expressed the state of our know- ledge when he said that the act of fertilization consisted in 'the union of identical parts of two homologous cells.' Pfluger's discovery of the ' isotropism' of the ovum was the first fact which distinctly pointed to the conclusion that the bodies of the germ-cells have no share in the transmission of hereditary tendencies. He showed that segmentation can be started m different parts of the body of the egg, if the latter be permanently removed from its natural position. This discovery constituted an important proof that the body of the egg consists of a uniform substance, and that certain parts or organs of the embryo cannot be potentially contained in certain parts of the egg, so that they can only arise from these re- spective parts and from no others. Pfliiger was mistaken in the urther interpretation, from which he concluded that the fertilized ovum has no essential relation to the organization of the animal subsequently formed by it, and that it is only the recurrence of the same external conditions which causes the 1 germ-cell to develope always in the same manner. The force of gravity was the first factor, which, as Pfliiger thought, de- ermined the building up of the embryo: but he overioked he fact that isotropism can only be referred to the body of the egg and that besides this cell-body there is also a nucleus present, from which it was at least possible that regulative' nfluences might emanate. Upon this point Born ^ first Showed hat the position of the nucleus is changed in eggs which are ^us placed in unnatural conditions, and he prffed that the i nucleus must contain a principle which in the first place ' ttr e 'T^^'T ^--^ further showed I that, even when the effect of gravity is compensated, he ^ Bo^n ^'w'^'- -^f V. ^3- p. 182, 1884. curage zum i-ntwicklungsmechanismus des Embryo,' 1884.