606 STUDIES IN GENERAL PHYSIOLOGY 



2 to 3 cells. It was not much better in the lot of eggs that 

 had been in this same solution for one hour and forty minutes. 

 The lot that had been in the solution two hours and forty-five 

 minutes had living blastulse, but not so many as the two lots 

 mentioned above. It is therefore obvious that the eggs of 

 different females show slight variations in the time required 

 for the eggs to remain in the mixture of 60 c.c. 2 n MgCl 8 

 -)- 40 c.c. sea-water in order to reach the blastula stage. 



I have thus far only spoken of eggs that had been in 

 solution 1. Of the eggs that had been in solution 2 not one 

 developed into a blastula. Those that had been in this 

 solution for two hours had not even segmented. Only the 

 eggs that had remained in that solution for two hours and 

 forty-five minutes showed a beginning of segmentation (2 

 cells), but only one in a thousand had segmented. It is 

 evident that either the amount of Mg ions or the total 

 osmotic pressure of the solution was too small to cause the 

 unfertilized eggs to develop. These experiments with 

 negative results are however very valuable as control experi- 

 ments against the possible contamination of the sea-water 

 with spermatozoa. If in such cases contamination had 

 happened, the eggs that had been in solution 2 ought to have 

 developed equally as well as, or better than, those that had 

 been in solution 1. The same remark might apply to the 

 preceding and following experiments. None of the eggs in 

 any of these solutions formed a membrane. 



Fourth series. In all the experiments in which blastulae 

 were produced from the unfertilized eggs three conditions 

 were united: (1) the total osmotic pressure of the artificial 

 solution was higher than that of sea- water; (2) the amount 

 of the Mg ions was increased; (3) the absolute amount of 

 the other ions normally present in sea-water was reduced. 

 In this series I desired to find out whether the third condi- 

 tion was essential, and whether the mere increase in the 



