f.r 



INFLUENCE OF HYDROGEN ION CONCENTRATION. 313 



water of pH 5.0 to 10.2 after an exposure of 10 minutes, very 

 little cytolysis or fragmentation occurs between pH 5.0 and 9.0. 

 At pH 9.3 there is a slight amount of fragmentation and a slightly 

 increased number of cytolyzed eggs. A large number of the eggs 

 are distorted from their normally spherical shape, showing that 

 they have softened. At pH 9.6 a few eggs are broken into smaller 

 fragments and the number of intact but cytolyzed eggs is dimin- 

 ished as compared with 9.3. At pH 9.9 the membrane and egg 

 cortex are abruptly destabilized and all the eggs are readily broken 

 into small, spherical and extremely stable fragments. 



Similarly the Arbacia egg is comparatively resistant to moderate 

 shaking between pH 5.8 and 9.3. At about pH 9.6 there is a 

 marked increase in the tendency to cytolyze. This egg does not 

 fragment as does the Asterias egg, presumably because of its in- 

 ability to form new surface films readily, but appears to cytolyze 

 rather slowly after rupture at some one point. From pH 9.6 to 

 10.2 the shaken suspensions are filled with ghosts and partially 

 cytolyzed eggs. 



THE MATURATION OF Asterias EGGS. 



The maturation of Asterias eggs is normally initiated as soon 

 as they are removed from the ovaries and come in contact with 

 sea water. The initiating factor or factors are not known. Loeb 

 (7) has shown, however, that the addition of acid to sea water 

 inhibits, and the addition of alkali favors the maturation process. 

 When slowed below a critical velocity the maturation process stops 

 and the eggs remain permanently immature. 



In view of the possible role of H- or OH-ions in initiating 

 maturation, an examination was made of the effects of increasing 

 acidity on the incidence of permanently immature eggs. The 

 eggs were introduced into the pH solutions without contact with 

 sea water by dipping small pieces of fresh ovary into the pH solu- 

 tions. After 45 minutes or an hour counts were made of the 

 mature and immature eggs, discriminating by the dissolution of 

 the wall of the germinal vesicle. A summary of experiments of 

 this nature is given in Table I. 



21 



