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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    VII. THE ANAPHASES. DIVERGENCE AND SEPARATION OF THE DAUGHTER-CHROMOSOMES. After the division is completed, the daughter-chromosomes have the form of short straight rods, placed with their long axes parallel to that of the spindle. They now rapidly separate, passing along the spindle-fibres until they come into actual contact with the centrosphere (Text-fig. XVII. A). The latter has meanwhile greatly increased in size and has a sharply defined boundary. Its substance is composed of a delicate reticulum, the meshes of which stain red with the double stain, while the astral rays are blue. The latter have now again extended themselves far out into the cytoplasm. The nature of the force by which the daughter-chromosomes are separated is still in dispute. The view generally prevailing among zoologists is that of Van Beneden, according to which the astral rays and spindle-fibres are contractile elements analogous to muscle-fibres. By contraction of the spindle-fibres the daughter-chromosomes, Fig. XVI. Fig. XVI. — The “anaphases”; divergence of the daughter-chromosomes (1000 diameters). A. The chromosomes in various stages of separation. In two of them the daughter-chromosomes are still united at one end. B. Divergence of the daughter-chromosomes. (Phototype 31.) to which they are attached, are believed to be mechanically dragged apart and transported to the spindle-poles. This view is supported by evidence so strong that it can scarcely be escaped in the case of some animal cells. Strasburger and some other botanists, on the other hand, maintain that there is no evidence in its favour in the case of plant-cells and regard the movement of the daughter-chromosomes as perhaps a chemotactic action caused by the formation of special chemical products at the spindle-poles. As the phototypes about to be described clearly show, the facts in Toxopneustes do not accord entirely with either of these views. Plate VIII. Phototype 30. Early Anaphase, shozving especially the Achromatic Structures. The daughter-chromosomes (not very sharply shown) are separating. The centrospheres have become sharply defined, and the reticulum is clearly shown. The astral rays are extending.