732 STUDIES IN GENERAL PHYSIOLOGY \ 
during the first few days also contained a small number of 
living transparent eggs. The latter were, without exception, 
immature. The experiment, therefore, shows that the mature 
eggs of starfish die in the course of a few hours, and that 
the cause of this death cannot be sought in the bacteria of 
the sea-water; and further, that under exactly the same con- 
ditions the immature eggs remain alive. 
Ill. THE CHEMICAL CONDITIONS NECESSARY FOR MATURA- 
TION IN STARFISH EGGS 
Since the eggs of Asterias are usually immature in the 
ovary, but, in part, at least, maturate in the course of one or 
two hours when introduced into sea-water, the suspicion was 
aroused that some of the substances contained in the sea- 
water brought about the maturation. In order to determine 
which substance this might be, a series of solutions were 
prepared having approximately the osmotic pressure of the 
sea-water. The result was so simple that it is not necessary 
to describe all the experiments here. For it was found that 
when the eggs are introduced into solutions which contain 
free hydroxyl ions, maturation soon follows, but that this 
does not occur in solutions containing no hydroxyl ions. 
So, for example, the eggs retain their nucleus in a $m NaCl 
solution, or in NaCl solutions to which some potassium or 
calcium has been added. If, however, 0.5 to 2 c.c. 7) 
NaOH is added to each 100 cc. of such solutions, matura- 
tion soon follows: that is to say, the nucleus becomes in- 
visible. Since sea-water contains free hydroxyl ions the 
conclusion is justified that these are one of the causes for 
the maturation of the starfish egg. It was possible to prove 
this assumption through further experiments. If a small 
amount of acid is added to sea-water, the free OH ions dis- 
appear, and the water becomes acid in reaction (through the 
addition of 1.5 ¢.c. or more ;", HCl to 100 c.c. sea-water). 
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