300 LOEB. 



taken from the same culture, and the percentage 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 that where the eggs lie together in a heap maturation occurs 

 slowly, but where they lie in a thin layer, maturation occurs 

 (juickly. This fact suggested the importance of oxyge-n for 

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

 the oxygen by the superficial layers of eggs prevents the diffusion 

 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 I 

 sea water which cause or accelerate maturation, oxygen and 

 hydroxyl ions. Possibly other constituents of the sea water are 

 also concerned in the process, but NaCl, Ca, and K have appar- 

 ently 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 matura- 

 tion of the eggs in the ovary. 



IV. THE PROLONGATION OF THE LIFE OF THE UNFERTILIZED 

 STARFISH EGG BY THE PREVENTION OF MATURATION. 



\Ve 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 immature eggs 

 remain alive a relatively long time. It was necessary now to 

 show that when the maturation of a culture of unfertilized egg of 

 Astcrias is prevented artificially, the eggs live longer. We begin 

 with the experiment which is technically most simple. The eggs 

 streaming from the ovary are divided into two portions. One 

 portion of eggs is carefully distributed without mechanical agita- 

 tion, by carefully tipping the vessel, in a thin layer over the bottom 



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

 Clepsine does not begin until after they are laid. Possibly the oxygen con- 

 tained in the water is in this case also a necessary condition for matura- 

 tion. 



