ARTIFICIAL PRODUCTION OF NORMAL LARV.E 585 



Mixtures of |n KC1 with y CaCl 2 allowed only the be- 

 ginning of the segmentation, and this only as long as CaCl 2 

 was used in very small quantities. In 96 c.c. KC1 + 4 c.c. 

 CaClg one egg in a thousand went into the two-cell stage, or 

 formed two large cells with two micromeres; but in 90 c.c. 

 KCl + 10 c.c. CaCl 3 not one egg segmented, and the solu- 

 tions with more Ca were not more favorable. 



A combination of -| NaCl with y n CaCl 2 was equally 

 poisonous. Even in 98 c.c. NaCl + 2 c.c. CaCl 2 the eggs 

 did not go beyond the beginning of the segmentation, and in 

 96 c.c. NaCl + 4 c.c. CaCl 2 the eggs died in the four-cell 

 stage. It is worthy of mention that in these solutions the 

 cleavage cells were very unequal in size. 



Mixtures of %n KC1 and -| NaCl were, on the other 

 hand, almost as favorable as the MgCl 2 solutions. In 98 c.c. 

 NaCl -f- 2 c.c. KC1 the eggs reached the sixty -four-cell 

 stage or went even beyond this. It was the same in 96 c.c. 

 NaCl + 4 c.c. KC1 for almost every egg divided. With 

 more KC1 and less NaCl the results were less favorable. 

 In a former paper we pointed out that the comparative 

 harmlessness of K ions for the phenomena of cell-division 

 is in striking contrast with the harmfulness of the same 

 ions for the phenomena of muscular contraction. We thus 

 see that the following two combinations of two chlorides 

 in solution are the most favorable for development: (1) 

 90 c.c. y n MgCl + 10 c.c. y n CaCl 3 ; and (2) 98 c.c. 

 -|n NaCl + 2 c.c. |n KC1. 



Three chlorides in solution. Neither with one nor with 

 two chlorides in solution was it possible to obtain swimming 

 blastulse. From the experience with Fundulus 1 I expected 

 that a combination of three metal ions (especially NaCl, 

 with small amounts of KC1 and CaCl 2 ) would allow the 

 eggs of the sea-urchin to complete their development. 



i Part II, p. 544. 



