THE INFLUENCE OF HYDROGEN ION CONCENTRA- 

 TION ON THE FERTILIZATION PROCESS IN 

 ARBACIA, ASTERIAS AND CHJETOPTERUS 



EGGS. 



HOMER W. SMITH AND G. H. A. CLOWES. 



(From the Lilly Research Laboratory, Indianapolis and the Marine Biological 



Laboratory, Woods Hole). 



In a previous communication we pointed out that when Asterias 

 and Arbacia eggs were inseminated in CO 2 -free sea water of 

 varying H-ion concentration, fertilization failed to occur in solu- 

 tions more acid than pH 6.6 to 7.0. This block to fertilization 

 appeared to be perfectly reversible, since eggs which did not 

 fertilize in solutions on the acid side of the block could be ferti- 

 lized when returned to solutions of greater alkalinity (i). Loeb 

 (2) has observed a similar block to fertilization in artificial salt 

 solutions. He found that Arbacia and 5". purpuratus eggs were 

 not fertilized in a neutral mixture of NaCl -j- MgCl 2 in the pro- 

 portion in which these salts exist in sea water. These eggs were 

 fertilized, however, if NaOH, NH 4 OH, benzylamine, butylamine 

 or NaHCO 3 were added to the NaCl + MgCl 2 mixture. The ad- 

 dition of CaCl 2 to the NaCl -f- MgCl 2 mixture similarly made 

 fertilization possible. The addition of NaOH or CaCl, to a 

 NaCl -(- KC1 mixture did not permit fertilization of all eggs, but 

 when both NaOH and CaCl 2 were added to a NaCl -f- KC1 mix- 

 ture as a rule all the eggs fertilized and began to divide. Since 

 cross fertilization can be effected between Asterias sperm and S. 

 purpuratus eggs by the addition of NaOH or CaCl 2 to normal 

 sea water, Loeb concluded that the act of diminishing the alkalin- 

 ity of the solution or of depriving it of CaCl 2 established the same 

 reversible block to the entrance of the homologous sperm as exists 

 for the entrance of the sperm of Asterias into S. purpuratus eggs 

 in normal sea water. Leob's experiments involve the change of 

 several variables at once, however, and it cannot be determined 

 from them to what extent the reaction of the external medium 



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