ARTIFICIAL PRODUCTION OF NORMAL LARV.E 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 larvae differed also in other respects from the larvae 

 produced from the unfertilized eggs. While the blastulce 

 of the fertilized eggs even after the treatment with solution 

 1 swam at the surface of the sea-water, the parthenogenetic 

 blastulce 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 blastulae in 

 these experiments died during the day. It goes without 

 saying that the blastulse which developed from the fertilized 

 eggs treated with solution 1 did not show the ragged con- 

 dition of the parthenogenetic larvae 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 c.c. \n MgCl 2 +40 c.c. sea- 

 water are able to develop into blastulae 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. ^n MgCl 2 ) 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 



