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==Centrosome.== Before noticing the activities of the nucleus it will be necessary to mention a third part of the cell. Within the last few years there has been found to be present in most cells an organ which has been called the centrosome.
The centrosome is too problematical as yet for much comment. It appears to be a piece of the machinery for bringing about cell division, but beyond this it is not safe to make any statements.
Previously to this process the other sexual cell, the spermatozoon, or male reproductive cell, has been undergoing a somewhat similar process. It contains cell substance, a nucleus with chromosomes, and a centrosome, the number of chromosomes, as shown later, being however only half that normal for the ordinary cells of the animals.
It is well known that the protoplasm of the cell effects various movements within its envelope; on the other hand, indirect cell-division is the outcome of very complex operations, some involving the nucleus and others the cytoplasm. These latter commence by the doubling of the centrosome, a small spherical body alongside the nucleus.
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