602 STUDIES IN GENERAL PHYSIOLOGY 



for the Arbacia egg is shown by the fact that the fertilized 

 eggs of Arbacia develop better in this solution than in 60 c.c. 

 2 n MgCl 3 -}- 40 c.c. sea-water. Hence it is evident that 

 the Mg ions alone were not able to bring about the develop- 

 ment of the unfertilized Arbacia eggs that had been in solu- 

 tion 1. Either the presence of other ions, such as are 

 contained in the 40 c.c. of sea- water or the increased osmotic 

 pressure in the mixture of 60 c.c. 2 -n MgCl 3 -(-40 c.c. sea- 

 water is essential for the development. The osmotic pres- 

 sure of a y n MgCl 2 solution is not very different from that 

 of sea-water. 



Second series. It was, of course, my next task to repeat 

 this experiment. I now knew which solution must be used 

 in order to obtain parthenogenetic blastulse, but I wanted to 

 find out how long the eggs must remain in this solution in 

 order to develop into a blastula. I put a quantity of 

 unfertilized eggs of one female into a solution of 60 c.c. 

 2 ^n MgCl 2 +40 c.c. sea- water at ten o'clock. At various 

 intervals a portion of these eggs was taken out of the solu- 

 tion and put back into 200 c.c. of normal sea-water. The 

 first lot was put back into normal sea-water after thirty 

 minutes. No egg had a membrane and none was seg- 

 mented. The second lot was put back into normal sea- water 

 after sixty-five minutes, the third lot after one hour and 

 forty minutes, the fourth after one hour and fifty minutes, 

 the fifth after two hours and five minutes, the sixth after 

 two hours and fifteen minutes, lot 7 after two hours and 

 thirty minutes, and the eighth lot after three hours and 

 fifteen minutes. The first, second, and eighth lots differed 

 much in regard to the time they were exposed to the artificial 

 solution from lots 3, 4, 5, 6, and 7, which were taken out of 

 the solution at much shorter intervals. No egg in any of 

 these solutions had any membrane or showed any trace of 

 segmentation at the time they were put back into normal 



