604 STUDIES IN GENERAL PHYSIOLOGY 
no blastule were left in lots 2 and 7, where they had at 
most been very scarce. The next morning only a few larve 
were left in lots 3 to 6, and these died during the day. 
I stated at the beginning of my experiments that only a 
part of the eggs of one female were put into the MgCl, 
solution. The others were left in normal sea-water to serve 
as control material. None of these eggs which were in the 
same sea-water as that used for the eggs treated with the 
MgCl, solution formed any membrane. After twenty-four 
hours a few eggs were found divided into 2 cells. No egg 
developed beyond this stage. 
This experiment shows that the time during which 
unfertilized eggs must remain in contact with a mixture of 
60 c.c. %,9n MgCl, + 40 c.c. sea-water in order to give rise 
to blastulz is limited in two directions. If the eggs remain 
only thirty minutes in such a solution, a few of them may 
begin to develop, but none will reach the blastula stage. But 
if the unfertilized eggs remain in this solution from one and 
one-half to two hours, more than 20 per cent., and ag many 
as 50 per cent., may develop, and the solution then teems 
with moving blastule, which however remain at the bottom 
of the dish. On the other hand the time limit will be 
exceeded if the eggs are left in the solution more than two 
and one-half or three hours. 
I tried another experiment in this series to see how soon 
the unfertilized eggs would lose their power of being affected 
by the MgCl, solution. The eggs were left in normal sea- 
water for eighty minutes, then put in a solution of 60 c.c. 
®n MgCl, + 40 cc. sea-water for two hours. Two hours 
later they were put back into normal sea-water. A large 
number of eggs began to segment, but I did not find any 
blastulee the next day. 
Third series.—Thus far I had found the right solution 
for producing blastulz from unfertilized eggs, and had found 
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