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 eggs 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, 



