540 STUDIES IN GENERAL PHYSIOLOGY 
(Arbacia) proceeded best in MgCl,, next best in KCl, while 
CaCl, proved to be the most injurious in the series. 
Seven years ago I, and later Norman, found that if the 
concentration of sea-water be raised sufficiently by the addi- 
tion of certain salts, a segmentation of the nucleus takes 
place without any segmentation of the protoplasm. Such 
eggs, however, when brought back into normal sea-water, 
divide into as many cells as there are preformed nuclei. 
This year I tried the effects of equimolecular solutions of 
MgCl,, KCl, NaCl, and CaCl, upon this process of nuclear 
division (in which the nuclear membrane is apparently 
liquefied), and found that the influence of the four salts 
(or rather kations) followed the order mentioned above. 
We know that enzymes as a rule require a slight degree 
of acidity or alkalinity for their action. I showed last year 
that the addition of a small amount of H ions to sea-water 
retards or prevents segmentation, while a small amount of 
HOions favors and accelerates thedevelopment of the Arbacia 
egg. 
2. It has been known for some time that the unfertilized 
eggs of echinoderms, worms, and arthropods begin to seg- 
wnent when left for a comparatively long time in sea-water. 
This has generally been considered a pathological phenom- 
enon. Mead succeded in causing a segmentation of the 
unfertilized egg of a marine worm, Cheetopterus, by the addi- 
tion of a very small amount of KCl to sea-water. Morgan 
tried the effect of more concentrated sea-water on the un- 
fertilized egg of sea-urchins, with results similar to those 
obtained by me previously with the same methods in fer- 
tilized eggs. If the unfertilized eggs are brought back from 
the more concentrated sea-water into normal sea-water, they 
break up into as many cells as there are nuclear masses pre- 
formed in the more concentrated solution. But in none of 
these cases did the cell-divisions of the unfertilized eggs lead 
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