734 STUDIES IN GENEKAL PHYSIOLOGY 



centage of mature eggs is determined, this percentage is 

 subject to the greatest variations. The cause of these 

 variations was soon discovered. For it was found where 

 the eggs lie together in a heap maturation occurs slowly, 

 but where they lie in a thin layer, maturation occurs quickly. 

 This fact suggested the importance of oxygen for matura- 

 tion. Where the eggs lie in a heap the appropriation of the 

 oxygen by the superficial layers of eggs prevents the diffu- 

 sion of the oxygen to those lying deeper. 



Experiments were now made in which the oxygen of a small 

 flask containing a small amount of sea-water was replaced 

 by hydrogen. When, in such experiments, all the oxygen 

 was entirely removed maturation did not occur in any, or at 

 least the majority of the eggs, in spite of the presence of 

 the hydroxyl ions in the sea- water. There are, therefore, at 

 least two substances in sea-water which cause or accelerate 

 maturation, oxygen and hydroxyl ions. Possibly other con- 

 stituents of the sea-water are also concerned in the process, 

 but NaCl, Ca, and K have apparently no beneficial effect upon 

 maturation. 1 



It seems, therefore, that the absence of oxygen and 

 hydroxyl ions in the ovaries belongs to the conditions which 

 inhibit maturation of the eggs in the ovary. 



IV. THE PROLONGATION OF THE LIFE OF THE UNFERTILIZED 

 STARFISH EGG BY THE PREVENTION OF MATURATION 



We have shown above that the mature eggs of a culture 

 of unfertilized starfish eggs die within a short time (which 

 decreases with an increase in temperature), while the imma- 

 ture eggs remain alive a relatively long time. It was 

 necessary now to show that when the maturation of a culture 

 of unfertilized egg of Asterias is prevented artificially, the 



1 Professor Whitman informs me that the maturation of the eggs of Clepsine 

 does not begin until after they are laid. Possibly the oxygen contained in the water 

 is in this case also a necessary condition for maturation. 



