Science2 - 00054

Science2 - 00054 - Untitled 1. An immature _sperm_-cell,...

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Untitled 1. An immature _sperm_-cell, with 4 chromosomes (nuclear bodies) represented as rods. 2. A mature sperm-cell, with 2 chromosomes. 3. An immature _egg_-cell, with 4 chromosomes represented as curved bodies. 4. A mature egg-cell, with 2 chromosomes. 5. The spermatozoon fertilises the ovum, introducing 2 chromosomes. 6. The fertilised ovum, with 4 chromosomes, 2 of paternal origin and 2 of maternal origin. 7. The chromosomes lie at the equator, and each is split longitudinally. The centrosome introduced by the spermatozoon has divided into two centrosomes, one at each pole of the nucleus. These play an important part in the division or segmentation of the egg. 8. The fertilised egg has divided into two cells. Each cell has 2 paternal and 2 maternal chromosomes.] [Illustration: _Reproduced from the Smithsonian Report, 1917._ GLASS MODEL OF A SEA-ANEMONE A long tubular sea-anemone, with a fine crown of tentacles around the mouth. The suggestion of a flower is very obvious. By means of stinging
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