ARTIFICIAL PRODUCTION OF NORMAL LARV.E 613 



undergo development, the solution with 60 c.c. MgCl 2 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 2 would still be favorable. A mix- 

 ture of 40 c.c. ^ n MgCl 2 + 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. 2 n MgCl 2 -\- 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 2 +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 n MgCl 2 . In the next experiments 

 the following four solutions were tried: 



(1) 55 c.c. ^-n MgCl + 45 c.c. sea- water 



(2) 50 +50 



(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 blastulse. Many of them resembled the blastulae of 

 Fig. 149, but the majority were clean and free from debris. 



