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It appears to the microscope similar to the cell substance in character, and has frequently been described as a bit of the cell substance more dense than the remainder. Lying within the nucleus there are usually to be seen one or more smaller rounded bodies which have been called nucleoli.
During this process of the formation of the chromosomes the nucleoli disappear, sometimes being absorbed apparently in the chromosomes, and sometimes being ejected into the cell body, where they disappear. Whether they have anything to do with further changes is not yet known. The next step in the process of division appears in the region of the centrosomes.
There is no difficulty in imagining the structure of our nervous system to be a priori, in regard to the excitements which are propagated in it. A nerve cell is formed, with its protoplasm, its nucleus and its nucleoli before being irritated; its properties precede its functions.
In many cells the nucleus is finely granular or reticulated in appearance, and on the threads of the meshwork may be one or more enlargements, called nucleoli. In some cases the protoplasm at the circumference is so modified as to give the appearance of a limiting membrane called the cell wall.
The typical form appears to be spherical or nearly so; but from this typical form they may vary, becoming irregular or elongated. The form and shape of the chromatin thread differs widely. The nucleii differ also in the number of nucleoli they contain as well as in other less important particulars.
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