ARTIFICIAL PropuctTion oF NorMat Larva 601 
shall discuss this point more fully in connection with the 
drawings. 
I have not yet mentioned one control experiment which I 
made in this series. I had one part of the eggs of the same 
female fertilized and put into the same four solutions for the 
same time as the unfertilized eggs. Every one of the ferti- 
lized eggs formed a membrane. The behavior of these eggs 
and their larve differed also in other respects from the larvee 
produced from the unfertilized eggs. While the blastule 
of the fertilized eggs even after the treatment with solution 
1 swam at the surface of the sea-water, the parthenogenetic 
blastulee were all at the bottom of the dish and unable to 
rise. This difference seems to be typical, as I found it in 
all my experiments. All the parthenogenetic blastule in 
these experiments died during the day. It goes without 
saying that the blastulee which developed from the fertilized 
eggs treated with solution 1 did not show the ragged con- 
dition of the parthenogenetic larve that had developed 
without a membrane. 
Unfertilized eggs that had been in solution 2 for one 
hour and fifty minutes were the next day unsegmented and 
without membrane. The unfertilized eggs that had been in 
solution 3 were all dead. The unfertilized eggs that had 
been kept in normal sea-water all the time were without a 
membrane and unsegmented. Thus it is evident that the 
unfertilized eggs of Arbacia, if put for one hour and fifty 
minutes in a solution of 60 cc. %2°n MgCl, + 40 c.c. sea- 
water are able to develop into blastulee which move about. 
But it is also evident from the control experiments that this 
cannot be due to the partial pressure or concentration of the 
Mg ions alone, for in solution 2 (100 c.c. 12 MgCl,) the 
concentration of the Mg ions was almost the same as in solu- 
tion 1, and yet no unfertilized egg was caused to segment by 
this solution. That the latter solution is not very poisonous 
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