It seems probable that the numerous researches of recent
years and others now in progress will open up a new world of
cell biology which will greatly advance our knowledge, especially
in the direction of increased depth and accuracy.
Fig. 1.—Nuclear division. A-H, karyokinesis of a tissue-cell. A, nuclear reticulum in its ordinary state. B, preparing for division; the contour is less defined, and the fibers thicker and less intricate. C, wreath-stage; the chromatin is arranged in a complicated looping round the equator of the achromatin spindle. D, monaster-stage; the chromatin now appears as centripetal equatorial V's, each of which should be represented as double. E, a migration of the half of each chromatin loop towards opposite poles of the spindle. F, diaster-stage; the chromatin forms a star, round each pole of a spindle, each aster being connected by strands of achromatin. G, daughter-wreath stage; the newly formed nuclei are passing through their retrogressive development, which is completed in the resting stage, H. d-f, karyokinesis of an egg-cell, showing the smaller amount of chromatin than in the tissue-cell. The stages d, e, f, correspond to D, E, F, respectively. The polar star at the end of the spindle is composed of protoplasm-granules or the cell itself, and must not be mistaken for the diaster (F). The coarse lines represent the chromatin, the fine lines the achromatin, and the dotted lines cell-granules. (Chiefly modified from Flemming.) X-Z, direct nuclear division in the cells of the embryonic integument of the European scorpion. After Blochmann (Haddon).
Though many points are still in dispute, it may be safely said that the nucleus plays, in most cells, a rôle of the highest importance; in fact, it seems as though we might regard the nucleus as the directive brain, so to speak, of the individual cell. It frequently happens that the behavior of the body of the cell is foreshadowed by that of the nucleus. Thus frequently, if not always, division of the body of the nucleus precedes that of the cell itself, and is of a most complicated character (karyokinesis or mitosis). The cell wall is of subordinate importance in the processes of life, though of great value as a mechanical support to the protoplasm of the cell and the aggre--
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