266 THE AMEBIC AX X. I TUBALIST [Vol. XLIX 



block to the entrance of the spermatozoon of Arbaria into 

 the egg of the same species as exists for the entrance of 

 the sperm of starfish into the egg of purpuratus in normal 

 sea water. 



Another form of the experiment may be mentioned. 

 When we put sperm and eggs of Arbacia (which had been 

 washed in an ra/2 NaCl solution) into a neutral mixture 

 of NaCl + KCl no egg can be fertilized although the 

 sperm may be so active and concentrated that the eggs 

 roll around in the solution and the chorion (the jelly sur- 

 rounding the egg) may be filled with spermatozoa. In 

 one experiment the eggs and sperm of Arbacia were kept 

 overnight in watch glasses containing 2.5 c.c. of this mix- 

 ture of neutral NaCl + KC1. The next morning all the 

 eggs were intact and not a single one was fertilized. At 

 that time 20 drops of sea water were added to the mixture 

 and instantly fertilization membranes were formed and 

 practically all the eggs segmented. 10 



It can be shown that in this experiment the sea water 

 added two important substances, Ca and NaOH. If 

 NaOH alone is added to the mixture of NaCl -f- KC1, as a 

 rule no egg is fertilized or only a few; if CaCl 2 is added 

 to a neutral mixture of NaCl + KCl a number of eggs 

 are fertilized. If both CaCl 2 and NaOH are added in the 

 proper proportion as a rule all the eggs are fertilized. 



It is perhaps important to call attention to the fact 

 that if eggs of Arbacia are fertilized in sea water and if 

 after repeated washings in a mixture of NaCl + KC1 or 

 of NaCl -f MgCl 2 they are put into these solutions they 

 will segment repeatedly in these solutions, thus showing 

 that the eggs were really not fertilized in these two so- 

 lutions in the above-mentioned experiments. 



The striking fact is again that the block created by the 



io This exper 



