The cell in development and inheritance / by Edmund B. Wilson.

  • Wilson, Edmund B. (Edmund Beecher), 1856-1939.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: The cell in development and inheritance / by Edmund B. Wilson. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    figure, except the minute asters, is formed inside it (Fig. 28). In ActinospJiceidimi, on the other hand, there is no true spireme stage, and no rod-shaped chromosomes are at first formed. The reticulum breaks up into a large number of granules which give rise to an equatorial plate, divide by fission, and are distributed to the daughter-nuclei. o.. Fig. 31. — Mhosis \n the rhizopod y4ciiKospk(ermm. [Brauer.] A. Nucleus and surrounding structures in the early prophase; above and beiow the reticular nucleus lie the semilunar pole-plates, and outside these the cytoplasmic masses in which the asters afterward develop. B. Later stage of the nucleus. D. Mitotic figure in the metaphase, showing equatorial plate, intra-nuclear spindle, and pole-plates {p.p.). C. Equatorial plate, viewed en face, consisting of double chromatin-granules. E. Early anaphase. F. G. Later ana- phases. //. Final anaphase. /. Telophase; daughter-nucleus forming, chromatin in loop-shaped threads; outside the nuclear membrane the cenlrosome, already divided, and the aster, y. Later stage; the daughter-nucleus established; divergence of the centrosomes. Beyond this point the centrosomes have not been followed. Only in the late anaphase {telophase) do these grannies arrange them- selves in tlireads (Fig. 31, /), and this process is apparently no more than a forernnner of the reticular stage. This case is a very convincing argument in favour of the view that the formation and splitting of chro- mosomes is secondary to the division of the ultimate chromatin-granules.