254 STUDIES IN GENERAL PHYSIOLOGY 
remained in normal sea-water. At 10:50 nearly all the eggs 
which had remained in normal sea-water were in the two-cell 
stage, while none of the eggs in the other solutions were yet 
segmented; in part (a) the first egg was segmented at 10:55; 
in (6) the first segmentation took place at 11:45—nearly an 
hour later than in normal sea-water; and in (c) no segmenta- 
tion at all took place. That the amount of water and the 
intra-cellular pressure in these experiments varied with the 
concentration could be seen from the form of the cleavage 
spheres. In normal sea-water, and still more in sea-water 
which was a little diluted by the addition of 10-20 per 
cent. of fresh water, the first two cleavage spheres were nearly 
perfect hemispheres. In sea-water of higher concentration 
the first two cleavage spheres became ellipsoidal in shape, 
approaching the sphere more the higher the concentration 
was. When I added more than 2 g. of NaCl to 100 cc. of 
sea-water, in a few hours plasmolysis took place, and the 
surface of the protoplasm began to shrink irregularly. But 
by bringing the eggs back into normal sea-water the normal 
form was restored in a few minutes. 
2. Further investigations concerning this subject led me 
to another series of facts, which, as I believe, give the physio- 
logical explanation of some of the phenomena of cleavage. 
In my investigations concerning the regeneration and growth 
of Hydroids, I found that a salt solution which is just con- 
centrated enough to prevent regeneration and growth by no 
means kills the Hydroids, or even annihilates the power of 
growth and regeneration. Hydroids which had been in 
such a solution for several days when brought back into normal 
sea-water began to regenerate and to grow. When I made 
the same experiments on fertilized eggs, the results were the 
same. A salt solution which is just concentrated enough to 
prevent segmentation does not annihilate the power of seg- 
mentation at once. But when I brought such eggs back . 
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