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. 



III. 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 -f- m NaCl 

 solution, or in NaCl solutions to which some potassium or 

 calcium has been added. If, however, 0.5 to 2 c.c. ^ 

 NaOH is added to each 100 c.c. 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.c. or more ^ HC1 to 100 c.c. sea-water). 



