INFLUENCE OF HYDROGEN ION CONCENTRATION. 319 



portion of eggs which recover their fertilizability. (The dashed 

 contour lines in Fig. 3 show the general course of this recovery 

 process. The figures written beside each curve show the duration 

 of the exposure to the pH solutions.) The block to fertilization 

 produced by short exposures to the solutions around pH 5.8 dis- 

 appears only when the eggs are left in the acid solutions. If re- 

 turned to sea water after a short exposure (i.e., 10 to 30 minutes) 

 the eggs remain permanently (4 to 6 hours) unfertilizable. 



Dr. Chambers has examined these eggs by microdissection and 

 finds that when treated for 5 minutes at pH 5.8 and then placed in 

 sea water, the membrane which envelops both the fertilized and 

 unfertilized egg is very much thickened and toughened. Longer 

 exposure to pH 5.8 tends to soften this membrane so that when 

 returned to sea water it is thin, delicate and easily torn. Though 

 the conclusion is by no means substantiated, it is possible that 

 this initial toughening of the membrane with subsequent softening 

 on longer exposure accounts for the inability of sperm to react 

 with short exposure as compared to long exposure eggs. 



That the sperm gain access to the egg after the block has worn 

 off is shown by the fact that without sperm they undergo at the 

 most two or three cleavages which are decidedly late and irregular, 

 while with sperm they develop with much more normal velocity 

 and with a quality that is so nearly normal that in many instances 

 they cannot be distinguished from normally fertilized eggs. 

 Many of them, moreover, develop into rough swimmers. There 

 is a marked tendency for the blastomeres to fuse in the later stages 

 with the production of syncytia ; and for the separate blastulae to 

 fuse, 4 or 5 forming one large, apparently homogeneous larva, or 

 for several to adhere together forming irregular chains. This 

 tendency for fusion, like the ameboid movements which accom- 

 pany activation and normal division, is clearly a consequence of 

 .some lability of the cortex. Fusion appears to be more marked 

 among those eggs exposed to solutions on the acid side of pH 5.8 

 than on the alkaline side. 



If we neglect the temporarily irreversible block created at pH 

 5.8, the optimum reaction for the retention of viability will prob- 

 ably be somewhere in this neighborhood, i.e., pH 5.8 to 6.0. It is 

 certain that this optimum is considerably on the acid side of sea 



