EXPERIMENTS ON CLEAVAGE 257 
lot, just as in the foregoing lots of the same kind, I found 
cleavage spheres of very different sizes in the same egg. At 
6:50 I repeated the same experiment, taking out a lot of 
eggs from the concentrated solution, and bringing them back 
into normal sea-water. Not one egg showed any trace of 
segmentation, but in a very short time—about twenty min- 
utes—the eggs segmented at once into a great number of 
small cleavage spheres, the smallest and most numerous having 
the size of a cleavage sphere of about the sixty-four-cell stage. 
I repeated this experiment about twenty times, always with 
the same result, which in a few words may be expressed as 
follows: If we bring impregnated egys into sea-water of a 
certain higher concentration, no segmentation takes place; 
but if we bring them back into normal sea-water, they divide 
in about twenty minutes directly into nearly, but not quite, 
so many cleavage spheres as they would contain by that 
time if they had remained in normal sea-water all the time. 
It must be added, however, that the normal eggs in this 
experiment are always ahead of the plasmolyzed eggs in 
regard to their stage of segmentation, and that their advance 
becomes the more obvious the farther they develop. 
Eggs, after having been in the concentrated solution from 
twelve to twenty-four hours, do not segment at all if brought 
back into common sea-water. All these experiments are the 
more satisfactory the better the material is. 
4, I varied these experiments by sometimes bringing the 
impregnated eggs into the concentrated solution immediately 
after impregnation, and sometimes later. The result remained 
the same, on the whole, and I will not dwell upon the details 
of these experiments. But the following fact may be of inter- 
est: I impregnated eggs in normal sea-water, and left them 
there until they were all in the two-cell stage. Then I 
brought them into the concentrated solution. The cleavage 
stopped directly. After having been there for three hours, 
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