6 ANIMAL PHYSIOLOGY. 
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, espe- 
cially in the direction of increased depth and accuracy. 
Though many points are still in dispute, it may be safely 
said that the nucleus plays; in most cells, a rdle 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 fre- 
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Fig. 1.—Nucuigar pivision. A-H, karyokinesis of a tissue-cell. A, nuclear reticulum in its or- 
dinary 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 be- 
ing 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 chro- 
matin than in the tissue-cell. The stages d, e, f, correspond to D, E, F, reepectirely The 
polar star at the end of the spindle is composed of protoplasm-granules of 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). 
quently, if not always, division of the body of the nucleus pre- 
cedes that of the cell itself, and is of a most complicated char- 
acter (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- 
