ARTIFICIAL PRODUCTION OF NORMAL LARVAE 583 



yn CaCl 3 with 10 c.c. of distilled water I occasionally saw 

 an egg in the two-cell stage. In more dilute CaCl 2 

 solutions no trace of a segmentation occurred. Hence Mg 

 and K were more favorable than Na and Ca ions for the con- 

 centration used in the experiments. It is very evident from 

 these experiments that the optimum concentration for each 

 of these four chlorides is different. 



In a f n LiCl solution the majority of eggs remained un- 

 segmented, and only very few reached the two-cell stage. 

 Mixtures of LiCl with sugar were no more advantageous. 

 In pure glycerin and sugar solutions of the same osmotic 

 pressure as that of a -|n NaCl solution no egg segmented. 

 It is evident that the quality of the ions is of more impor- 

 tance in these experiments than the osmotic pressure, and 

 that NaCl is not an indifferent substance. 



Two chlorides in solution. In a solution of one chloride 

 the eggs of Arbacia cannot reach the blastula stage. Are 

 mixtures of two chlorides more favorable for segmentation? 

 Among the possible mixtures of the two chloride solutions 

 of the same osmotic pressure as the sea-water I found those 

 between *- n MgCl 2 and J n CaCl 2 the most favorable. 

 The following twelve mixtures were prepared : ! 



(1) lOOc.c. V^MgCl 2 + Oc.c. J^wCaCla 



(2) 95 " +5 



(3) 90 " +10 



(4) 80 " +20 " 



(5) 70 " + 30 " 



(6) 60 " + 40 



(7) 50 " + 50 



(8) 40 " + 60 



(9) 30 " + 70 " 



(10) 20 " + 80 



(11) 10 " + 90 



(12) " +100 



1 It will save repeating these figures if I may state here that the same twelve 

 proportions were used in all the following experiments with two chlorides in 

 solution. 



