EXPERIMENTS ON CLEAVAGE 268 
the nucleus which also may be effective if separated from the 
nucleus. 
8. The physiological causes of the segmentation of the 
nucleus are not directly touched by these experiments. But 
two points ought to be mentioned: first, that the segmenta- 
tion of the nucleus in the concentrated solution (2 g. of NaCl 
to 100 c.c. of sea-water) was retarded, and at last ceased 
entirely after from twelve to twenty-four hours; secondly, 
that the segmentation. of the nucleus was extremely irregular 
when the protoplasm did not take part in segmentation. We 
see in these facts some of the influences which the proto- 
plasm exercises on the segmentation of the nucleus. This 
influence may be exercised in this way, that by the high 
intra-cellular pressure which normally exists in the cleavage 
spheres these spheres press and flatten each other. The form 
of the cell, however, determines, as Sachs showed long ago, 
the orientation of the plane of division, and, as Hertwig 
believes, in such a way that the longitudinal axis of the 
Kernspindel is put in the longest diameter of the cell. 
Therefore we ought to expect that, within certain limits, with 
increasing intracellular pressure, Sach’s law of the rectangu- 
lar division of the planes of cleavage would become more 
obvious. I found, indeed, that in normal, or still more in 
somewhat diluted, sea-water, where the turgor, and conse- 
quently the flattening of the cleavage spheres, was the great- 
est, Sach’s law was the most exactly realized. Therefore this 
geometrical regularity in the segmentation of the nucleus 
which is so striking under normal conditions must disappear 
at once if the protoplasm does not take part in segmentation. 
9. Our observations concerning the dependence of irrita- 
bility of the protoplasm upon the water contained in the tis- 
sues add one more fact to those given already to explain the 
importance of water for all processes of growth and develop- 
ment. If we reduce the amount of water in aregenerating or 
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