596 STUDIES IN GENERAL PHYSIOLOGY 



existence of a membrane may serve to show whether eggs 

 were fertilized or not. The fertilized eggs that were put 

 into the second solution (KC1) did not reach the blastula 

 stage. They stopped at about the thirty-two- to the sixty- 

 four-cell stage. Those that had been in the third solution 

 (NaCl) were in about the same condition, with the exception 

 perhaps that at first the segmentation was more unequal. 

 In the fourth solution (CaCl 2 ) no egg segmented, and only 

 one egg in a thousand showed a beginning of segmentation, 

 consisting of an incision at one side of the egg. 



I finally wished to know how fertilized and unfertilized 

 eggs behaved if left for eighteen hours in a mixture of 

 60 c.c. 2 n MgCl 2 +40 c.c. sea-water. The unfertilized 

 eggs formed no membrane, but a very large part, more 

 than 50 per cent., of the eggs was divided into from 2 to 8 

 cells. The fertilized eggs had a membrane. In regard to 

 segmentation there was little difference between the two lots. 

 It was especially this circumstance which made me hope 

 that with a little more care it would be possible to raise liv- 

 ing larvae from unfertilized eggs by treating them with a 

 suitable mixture of 2 -^ n MgCl 3 solution and sea-water. 



In these and other similar experiments, which I will not 

 describe, it was moreover evident that after the treatment 

 with Mg ions the character of the segmentation was much 

 more normal than after the treatment with K and Na or Ca 

 ions. The K ions were nearest the Mg ions in their effect. 

 The Ca ions were the most unfavorable. The former experiments 

 of Norman had also yielded the result that the Mg ions were 

 the most harmless for the segmentation of the sea-urchin egg. 



IV. THE ARTIFICIAL PRODUCTION OF NORMAL LARVJ2 (PLU- 

 TEl) FROM THE UNFERTILIZED EGG OF THE SEA-URCHIN 



The most serious danger in experiments with unfertilized 

 eggs is the possibility that the sea-water or the instruments 



