UNFERTILIZED STARFISH EGGS. 



299 



c.c. of such solutions, maturation soon follows : that is to say, the 

 nucleus becomes invisible. 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 disappear, and the 

 water becomes acid in reaction (through the addition of 1.5 c.c. 

 or more n/io HC1 to 100 c.c. sea water). Immature eggs 

 were introduced directly into sea water to which I, 2, 3 and 

 4 c.c. of an n/io 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 I 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 n/io 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 eggs. 1 



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 XaHCO 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 con- 

 centration of the free hydroxyl ions in the sea water. 



But the hydroxyl ions are certainly not the only substances in 

 the sea water which favor or cause the maturation of the star- 

 fish egg. I soon found that when different specimens of eggs are 



1 Loeb, Fischer, and Xeilson, Pfliiger's Archiv, 1901, Bd. 87. 





