254 STUDIES IN GENEEAL 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 (b) 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 mofe than 2 g. of NaCl to 100 c.c. 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 



