. An atlas of the fertilization and karyokinesis of the ovum. Ovum; Fertilization (Biology); Meiosis; Embryology -- Echinodermata. iiiii!ii^:;-;';>v-:V:Vfiijii^-.:^ B Fig. IV. l-ic IV — \ The two aerm-iiuclei in the egg of the gastropod Plerotrachea. Highly magnified, after Boveri. E, the egg-nucleus; S, the sperm-nucleus, each containing sixteen elongated chromosomes. PB, the polar bodies. The centrosome has divided into two to form an amphiaster. Its origm m this animal has not yet been determmed. i;. Later stage, showing the fully developed amphiaster. Above it lie the sixteen maternal c
. An atlas of the fertilization and karyokinesis of the ovum. Ovum; Fertilization (Biology); Meiosis; Embryology -- Echinodermata. iiiii!ii^:;-;';>v-:V:Vfiijii^-.:^ B Fig. IV. l-ic IV — \ The two aerm-iiuclei in the egg of the gastropod Plerotrachea. Highly magnified, after Boveri. E, the egg-nucleus; S, the sperm-nucleus, each containing sixteen elongated chromosomes. PB, the polar bodies. The centrosome has divided into two to form an amphiaster. Its origm m this animal has not yet been determmed. i;. Later stage, showing the fully developed amphiaster. Above it lie the sixteen maternal chromosomes, below it the sixteen paternal, the nuclear membranes having disappeared. form of cell-division (from which the cleavage of the ovum differs only in the fact that it is preceded by a fusion of two cells) involves a complicated process known as karyokinesis or mitosis. This is characterized by the appearance of a structure known as the karyokiuctic figure (Text-fig. V. B), derived partly from the nucleus and partly from the surrounding cell-protoplasm or cytoplasm. The karyokinetic figure consists of two elements. One of these, the achromatic figure or amphiaster, consists of a fibrous spindle-shaped structure or spindle, at either pole of which is a star or aster consisting of fibres or rays radiating into the cytoplasm, the whole figure strongly suggesting the arrangement of iron filings about the poles of a horseshoe magnet. The centre of each aster is occupied by a rounded mass known as the centrosome or centrosphere, which is derived from that of the resting-cell, and like the latter may contain one or more centnoles. The entire substance of the amphiaster is often designated as archoplasm, but this term is strictly applied to the substance of the astral rays and spindle-fibres alone. The second, or chromatic, portion of the karyokinetic figure is derived from the nucleus, and consists cf chromosomes like those arising from the germ-nuclei, which are grouped ab
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Keywords: ., bookauthorwilsoned, bookcentury1800, bookdecade1890, bookyear1895
