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

  • Edmund Beecher Wilson
Date:
1902, ©1900
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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    origin, since the ends of the spindle begin to form before dissolution of the nuclear membrane, and the latter is pushed inwards in folds by the ingrowing fibres (Figs. 25, C, 99).^ In some cases, however, it seems certain that the nuclear membrane fades away before com- pletion of the spindle (first maturation-division of Thalassema, Chce- topteriLs), and it is probable that the middle region of the spindle is here formed from the linin-network. In most, if not all, mitoses of the second type the chromosomes do not form a ring about the equator of the spindle, but extend in a fiat plate completely through r \> Fig. 32. — Mitosis in Sfypocatilon. A. Early prophase with single aster and centrosome. spindle. C. Divergence of the daughtej--centrosomes. still intact. [Swingle.] B. Initial formation of intranuclear D. Early anaphase; nuclear membrane its substance. Here, therefore, it is impossible to speak of a cen- tral spindle. It is nevertheless probable that the spindle-fibres are of two kinds, viz. continuous fibres, which form the interzonal fibres seen during the anaphases, and half-spindle fibres, extending only from the poles to the chromosomes. It is possible that these two kinds of fibres, though having the same origin, respectively corre- 1 Cf. Plainer ('86) on Arion and Lepidoptera, Watase ('91) on Loligo, Braus ('95) on Triton, and Griffin ('96, '99) on Thalassema. Erlanger ('97, 5) endeavours to show that in the mitosis of embryonic cells in the cephalopods (Sepia), where the inpushing of the mem- brane was previously shown by Watase, the entire spindle arises from the nucleus. G