INFLUENCE OF HYDROGEN ION CONCENTRATION. 32! 



fluids of Astcrias and Arbacia are approximately neutral and it is 

 unlikely that at any time the egg would naturally be subjected to 

 an acidity so great as pH 6.0. 



SUMMARY. 



A method is described for preparation of CCX-free sea water 

 of H-ion concentrations from pH 4.5 to 10.2. 



The eggs of Asterias, Arbacia and Choztopierus retain for the 

 longest time their capacity to fertilize and to divide at about pH 

 6.0. 



Approximately this same H-ion concentration is required to 

 completely repress the maturation process in Asterias eggs. 



Chatopterus eggs are activated by exposures of 30 minutes or 

 more to solutions of pH 5.0 to 6.6. If left in these solutions they 

 show marked ameboid movements and fragmentation, but do not 

 divide. If returned to sea water half or more of the eggs will 

 undergo one or two abortive divisions. The activating effect of 

 the acid sea water is most intense at about pH 5.8 to 6.0. 



An exposure of 5 or 10 minutes to solutions of pH 5.0 to 6.6 

 (which is insufficient to activate) creates a block to fertilization 

 which is permanent if the eggs are returned to sea water. If left 

 from 30 minutes to several hours in the acid sea water, these eggs 

 gradually recover their fertilizability, and when inseminated de- 

 velop almost normally. 



We are indebted to Mabel T. Studebaker for the statistical 

 work in the experiments recorded in this paper. 



BIBLIOGRAPHY. 



1. Clowes, G. H. A. and Smith, Homer W. 



'23 Air.er. J. Physiol., XLIY., 144. 



2. Clark, Win. Mansfield. 



'20 The Determination of Hydrogen Ions. Baltimore. 



3. McClendon, J. F. 



'17 J. Biol. Chein., XXX., 265. 



4. Lillie, Ralph S. 



'18 BIOL. BULL., XXII., 328. 



5. Goldfarb, A. J. 



'18 BIOL. BULL., XXXIV., 372. 



6. Chambers, Robert. 



'17 Amer. J. Physiol., XLIII., i. 



