NATURAL DEATH AND FERTILIZATION 733 



Immature eggs were introduced directly into sea-water to 

 which 1, 2, 3 and 4 c.c. of a ^ HNO 3 solution had been 

 added to each 100 c.c. of sea- water. While, as is usual, a 

 large percentage of eggs soon maturated in the normal sea- 

 water, maturation did not occur at all in the vast majority or 

 in all the eggs contained in the sea- water to which 2 or more 

 c.c. acid had been added. The addition of even 1 c.c. of 

 acid diminishes the number of eggs that maturate. But it is 

 not even necessary to keep the eggs permanently in neutral 

 or acid sea-water in order to inhibit maturation. If 4 or 5 c.c. 

 of a ^ HNO 3 solution are added to 100 c.c. sea- water, and 

 immature eggs are introduced into such a solution for only 

 about fifteen minutes, relatively few eggs maturate when 

 they are returned to normal sea-water. Such acidified sea- 

 water does not kill the starfish eggs. 



We shall see later that the procedure described here 

 which, when used upon immature eggs, prevents maturation, 

 brings about artificial parthenogenesis when used on mature 



I have, moreover, been able to convince myself of the 

 fact that the eggs which are introduced into acidified sea- 

 water in an immature state, can be fertilized by sperm if 

 they finally maturate. It is possibly in harmony with what 

 has just been said that the addition of NaHCO 3 , or larger 

 amounts of sodium citrate to the sea-water accelerates the 

 process of maturation. Free hydroxyl ions are present in the 

 solutions of both substances, and it is possible that their 

 addition to the sea-water increases the concentration of the 

 free hydroxyl ions in the sea-water. 



But the hydroxyl ions are certainly not the only sub- 

 stances in the sea-water which favor or cause the maturation 

 of the starfish egg. I soon found that when different speci- 

 mens of eggs are taken from the same culture, and the per- 



i LOEB, FISCHER, AND NEILSON, Pfl&gers Archiv, Vol. LXXXVII (1901), p. 594. 



