form. The nucleus is accordingly, in cells of all shapes, that part which is the most constantly found unchanged. There are indeed isolated cases, which lie scattered throughout the whole series of facts in comparative anatomy and pathology, in which the nucleus also has a stellate or angular appearance; but these are extremely rare exceptions, and dependent upon peculiar changes which the element has undergone. Generally, it may be said that, as long as the life of the cell has not been
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brought to a close, as long as cells behave as elements still endowed with vital power, the nucleus maintains a very nearly constant form.
The nucleus, in its turn, in completely developed cells, very constantly encloses another structure within itself—the so-called nucleolus. With regard to the question of vital form, it cannot be said of the nucleolus that it appears to be an absolute requisite; and, in a considerable number of young cells, it has as yet escaped detection. On the other hand, we regularly meet with it in fully developed, older forms; and it, therefore, seems to mark a higher degree of development in the cell. According to the view which was put forward in the first instance by Schleiden, and accepted by Schwann, the
Fig. 3. a. Hepatic cell. b. Spindle-shaped cell from connective tissue, c. Capillary vessel, d. Somewhat large stellate cell from a lymphatic gland, e. Ganglion-cell from the cerebellum. The nuclei in every instance similar.
