ARTIFICIAL PRODUCTION OF NorMAL Larva 613 
undergo development, the solution with 60 ¢c.c. MgCl, and 
40 c.c. sea-water is equally good or even better than the 
mixture of equal parts of both. I now tried whether a 
mixture with less MgCl, would still be favorable. A mix- 
ture of 40 c.c. %2n MgCl, +60 c.c. sea-water was found 
ineffective. The eggs remained two hours in this solution, 
and a few of them segmented afterwards, but as the number 
was comparatively small I did not follow up this experiment. 
It is possible that a mixture of 40 c.c. %,9n MgCl, + 60 c.c. 
sea-water is too weak to bring about artificial partheno- 
genesis of the egg of Arbacia. In one of the preceding 
experiments we found that by treating the eggs with a 
mixture of 30 c.c. 2,°n MgCl, +60 c.c. sea-water we were 
not able to bring about parthenogenesis. 
Eighth series.—It was evident that in order to produce 
plutei from the unfertilized egg of Arbacia we must confine 
ourselves to solutions which contain less than 60 and more 
than 40 per cent. of 2.2n MgCl,. In the next experiments 
the following four solutions were tried: 
(1) 55 cc. 4°” MgCl + 45 e.c. sea-water 
(2) 50 = + 50 a 
(3) 45 «“ + 55 «“ 
(4) Normal sea-water 
. At three different intervals (two hours, two hours and 
ten minutes, two hours and twenty minutes) portions of the 
eggs were taken out of these four solutions and put back 
into normal sea-water. Two hours later in each of the lots 
that had been in the first three solutions about 50 per cent. 
of the eggs were segmented into from 2 to 16 cells. None 
of them had a membrane. No egg in solution 4 (normal 
sea-water) was segmented or had a membrane. The next 
morning the eggs that had been in solution 1 were teeming 
with blastule. Many of them resembled the blastule of 
Fig. 149, but the majority were clean and free from débris. 
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