Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 m â * -V 5 6 7 Fig. 244. The nucleus in cell division /, Diagram of a cell with the chromatin in a tangle, or network ; before cell division the chromatin assumes the form of a continuous thread. The thread breaks up into a definite number of pieces, or c/iromosomes, 2 ; the number of these is constant for any given species of plant or animal. The chromosomes arrange themselves in a central ring, J ; the membrane inclosing the nucleus disappears ; fine threads
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 m â * -V 5 6 7 Fig. 244. The nucleus in cell division /, Diagram of a cell with the chromatin in a tangle, or network ; before cell division the chromatin assumes the form of a continuous thread. The thread breaks up into a definite number of pieces, or c/iromosomes, 2 ; the number of these is constant for any given species of plant or animal. The chromosomes arrange themselves in a central ring, J ; the membrane inclosing the nucleus disappears ; fine threads appear to connect the chromosomes with tiny bodies at opposite ends of the cell. Each chromosome splits in two lengthwise, 4. The members of each pair move from each other to opposite ends, J. The half-chromosomes form two new tangles, 6, and gradually lose their definition. The new masses of chromatin become the nuclei of two new cells, 7 lengthwise (see Fig. 245). As a result of these two divisions, which usually follow each other in rapid succession,^ the egg cell contains one foiirth of the chromatin present in the cell from which it was formed, and only one half of the nsual mmiber of chromosomes. The division which separates the 1 It is believed that in some cases the splitting of the chromosomes takes place before the separation into the reduced numbers.
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