ARTIFICIAL PRODUCTION OF NORMAL LARV.E 595 



c.c. sea-water) also began to segment. The next morning about 

 1 per cent, of the eggs were divided into from 2 to 4 cells. 

 They were all without membranes, but they looked less normal 

 than the MgCl 2 eggs, and soon began to disintegrate. 



The third lot of eggs had been in 60 c.c. NaCl-j-40 c.c. 

 sea-water. Practically none of these eggs segmented during 

 the next twenty-four hours, and none formed a membrane. 

 The fourth lot of eggs had been in 60 c.c. CaCl 2 +40 c.c. 

 sea-water. A few of these showed a beginning of segmen- 

 tation, but every egg had a membrane. I have found since 

 that in pure CaCl 2 solutions of even lower concentration 

 unfertilized eggs form a membrane. It is possible that the 

 formation of a membrane consists in a process of coagula- 

 tion which is favored by Ca ions. 1 



I made a parallel series of experiments with fertilized 

 eggs of the same female. The eggs were, as usual, fer- 

 tilized in normal sea-water, and five minutes later were put 

 into the various solutions. The eggs were divided into 

 four lots, and put into solutions of the same character as in 

 the above-mentioned experiment with unfertilized eggs. 

 Like the unfertilized eggs, the fertilized eggs remained in 

 the solution one hour and fifty minutes. When brought 

 back into normal sea-water those that had been in solu- 

 tion 1 (60 c.c. MgCl 2 + 40 c.c. sea- water) began to divide in 

 fifteen minutes. The segmentation was very regular. Two 

 hours and forty-five minutes later every egg was segmented 

 into from 8 to 32 cells. Every egg had a membrane. The 

 next morning a large number of eggs swam about in the 

 blastula stage, still having a membrane. This observation is 

 of importance, as it shows that even in eggs that were in a 

 mixture of 60 c.c. 2 n MgCl 2 with 40 c.c. sea-water the 



1 Hertwig showed that unfertilized eggs form a membrane in water saturated 

 with chloroform. Herbst found that benzol, toluol, and xylol bring about the same 

 effect. All these media have a coagulating effect. HERBST, Biologisches Central- 

 blatt. Vol. XIII (1892), p. 14. 



