606 STUDIES IN GENERAL PHYSIOLOGY 
2 to 8 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 blastulz, 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 cc. 2,°n MgCl, 
+ 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 blastule 
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 
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