An introduction to the study of the comparative anatomy of animals . t oppositepoles. As it divides and travels round, each moiety of thecentrosome becomes surrounded by a number of radiatingfibrillae stretching into the adjoining protoplasm, and so forming a characteristic star-shaped figure to which the name ofthe astral figure has been given, the fibrillae being known asthe astral rays. There is some doubt as to whether the astralrays are formed entirely from the centrosphere or from theordinary cytoplasm. , Meanwhile important changes have been going on in thechromatic reticulum of the nuc
An introduction to the study of the comparative anatomy of animals . t oppositepoles. As it divides and travels round, each moiety of thecentrosome becomes surrounded by a number of radiatingfibrillae stretching into the adjoining protoplasm, and so forming a characteristic star-shaped figure to which the name ofthe astral figure has been given, the fibrillae being known asthe astral rays. There is some doubt as to whether the astralrays are formed entirely from the centrosphere or from theordinary cytoplasm. , Meanwhile important changes have been going on in thechromatic reticulum of the nucleus. The network breaks upand resolves itself into a convoluted thread composed entirelyof chromatin, which now stains even more intensely thanbefore. The convoluted thread at this stage is known as theskein or spireme. In a short time the spireme breaks up into Digitized by Microsoft® MITOSIS 3 a number of segments of equal length, which may be straightand rod-shaped, or curved into a horseshoe shape, or maybe simply spherical or ovoid masses. In some cases the. Fig- 23- Diagrams representing the essential phenomena of mitosis. A, a cell with restingnucleus containing a chromatic reticulum and a single nucleolus. Thecentrosome is double and surrounded by the centrosphere. £, the centro-somes are separating and each is surrounded by astral rays ; the chromatinforms a convoluted thread or spireme. C, The spireme is broken up into anumber of V-shaped chromosomes, the polar spindle is formed between thenow widely separate centrosomes. D, The chromosomes attached to thespindle-fibres are arranged at the equator of the spindle. £, division of thechromosomes, which are viewed end on. J^, divergence of the , chromosomes collecting at the poles of the spindle, the space betweenthem occupied by interzonal fibres ; commencement of division of the cell-body. If, /, complete division of the cell, and reconstitution of the / the centrosomes are dividing preparator
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