An atlas of the fertilization and karyokinesis of the ovum / by Edmund B. Wilson ; with the cooperation of Edward Leaming.

  • Leaming Edward, 1861-1916.
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: An atlas of the fertilization and karyokinesis of the ovum / by Edmund B. Wilson ; with the cooperation of Edward Leaming. 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.

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    These facts justify the conclusion that the nuclei of the two germ-cells are in a morphological sense precisely equivalent, and they lend strong support to Hertwig's identification of the nucleus as the bearer of hereditary qualities. The precise equivalence of the chromosomes contributed by the two sexes is a physical correlative of the fact that the two sexes play, on the whole, equal parts in hereditary transmission, and it seems to show that the chromosomal substance, the chromatin, is to be regarded as the physical basis of inheritance. Now, chromatin is known to be closely similar to, if not identical with, a substance known as nuclein (C29 H49 N9 P3 022, according to Miescher), which analysis shows to be PB D Fig. III. Fig. III. — History of the germ-nuclei in the thread-worm Ascaris megalocephala (after Boveri), highly magnified. A. Egg immediately after the formation of the second polar body, PB; E, the egg-nucleus, consisting of two branching chromosomes; S, the sperm-nucleus derived from the head of a spermatozoon that has entered the egg. B. Following stage, in which the egg-nucleus (E) and sperm-nucleus (S) have assumed the same size and structure. C. Later stage, in which the substance of each germ-nucleus has become transformed into tu'o chromosomes,— i.e., each sex has contributed two of these bodies, exactly similar in form and size. On either side, at A, is an attraction-sphere or archoplasm-sphere, each containing a single centrosome. These were originally supposed by Van Beneden to be derived one from each sex. Boveri showed that the two arise by the division of one sphere, which is developed under the influence of a centrosome, derived from the spermato- zoon alone. D. The karyokinetic figure forming for the first cleavage. The archoplasm-spheres have given rise to two asters (A) between which a spindle (S) is forming. The chromosomes (C) are splitting lengthwise, the two halves being destined respectively for the two daughter-cells. a tolerably definite chemical composed of nucleic acid (a complex organic acid rich in phosphorus) and albumin. And thus we reach the remarkable conclusion that inheritance may, perhaps, be effected by the physical transmission of a particular chemical compound from parent to offspring. Structure of the Resting-cell. — It is now necessary to consider briefly, the structure of the resting-cell as an introduction to the subject of cell-division, which, in turn, leads us to another aspect of fertilization. In the resting-cell (Text-fig. V. A) the protoplasm of the cell-body, ox cytoplasm, consists of a network or cyto-rcticulum