2^6 LOEB. [Vol. VII. 



At 2.40 I brought another lot of eggs from the concentrated 

 solution back into normal sea-water. Not one o,^^ showed seg- 

 mentation. At 2.50 the segmentation began. Just as in the 11 

 o'clock lot, hardly one egg segmented into two cleavage spheres. 

 But whilst most of the eggs of the 1 1 o'clock lot segmented 

 into from four to eight cells, most of the eggs segmented now 

 into from eight to sixteen cleavage spheres at once. The num- 

 ber and size of the cleavage spheres varied again in the different 

 eggs, but the striking feature this time was the prevalence of 

 cleavage spheres of the size of the sixteen-cell stage. The normal 

 eggs by this time came into the morula stage. At 4.05 another 

 lot of eggs was brought back from the concentrated solution 

 into normal sea-water. Not one o.g'g had segmented. Twenty 

 minutes later, however, nearly all the eggs were in cleavage. But 

 this time they did not divide into sixteen, but into many more 

 segments at once. I think that most of the eggs showed about 

 thirty cleavage spheres. Of course in this 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 minutes — 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 rcjnained in normal sea-ivater 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. 



