640 STUDIES IN GENERAL PHYSIOLOGY 



KC1 solution only a comparatively small number of eggs 

 reached the blastula stage, certainly many less than in my 

 previous experiments with MgCl 2 on Arbacia. A further 

 examination revealed the fact that the MgCl 2 solution 

 which I had used was, through an error or a misunder- 

 standing of the assistant who made it, weaker than a 2 n 

 solution. As soon as I found this out, I started experi- 

 ments with more diluted NaCl and KC1 solution. Instead 

 of using equal parts of a y n NaCl or KC1 solution and 

 sea-water, I used the following mixtures: 



20 zg-n NaCl + 30 distilled water + 50 sea-water, 

 or- 171 2g. n N a Q _j_ 32^ distilled water + 50 sea-water. 



In both cases more eggs reached the blastula and pluteus 

 stage than with the original stronger mixture. In one case 

 unfertilized eggs developed beautifully after having been 

 for two hours in a solution of equal parts of 15 2^n NaCl 

 -f- 35 distilled water + 50 sea-water. But this was nearly 

 the lowest limit for artificial parthenogenesis in Arbacia. 

 As a rule, 25 per cent, or more of the unfertilized Arbacia 

 eggs reached the blastula stage. 



3. It was thus proved that MgCl 3 does not play a specific 

 role in the production of artificial parthenogenesis. It 

 remained to decide whether it is essential to remove one 

 part of the normal constituents of the sea-water, or whether 

 the mere increase of the osmotic pressure suffices. I found 

 that the increase in the osmotic pressure of the sea-water is 

 all that is needed. In the experiments in which the maximal 

 number of unfertilized eggs reached the bastula stage about 

 1 gram NaCl had been added to the sea-water. "We can 

 produce the same increase in the osmotic pressure of the 

 sea- water by adding 10 c.c. of the 2%n NaCl or 2%n KC1 

 solution 1 to 90 c.c. of sea- water. In this case the mixture 



i My 2Un NaCl solution contained 146.25 g. in a liter. The 2>4?iKCl solution 

 contained 186.25 g. in a liter. 



