388 E. E. JUST. 



on restoral to normal sea-water. Such an optimum lies around 

 22 parts zYz M NaCl or KC1 plus 78 parts sea-water. The solu- 

 tions 20, 22, and 24 parts 2 T / 2 M NaCl or KC1 plus So. 78, and 76 

 parts sea-water, respectively, were the ones used most extensively. 

 In general, portions of eggs from one female were exposed to each 

 of these concentrations to cover any variation of the eggs with 

 respect to their response to treatment with hypertonic sea-water, 

 since these concentrations are around the optimum. The follow- 

 ing table summarizes results of a part of the forty experiments on 

 this point. It is scarcely necessary to say that in all this work 

 extreme precautions were taken against accidental insemination. 

 In none of the experiments did the control, uninseminated eggs in 

 sea-water, show a single membrane. 



TABLE I. 



EFFECT OF KYPEETONIC SEA-WATER ON EGGS OF ARBACIA AS SHOWN BY THE 

 PER CENT. OF EGGS THAT SEPARATE MEMBRANES WHILE IN THE HYPER- 

 TOXIC SEA-WATER. 



Date Per Cent, of 2| M NaCL 1 Per Cent, of Eggs 



of in Sea-water to which that Separate 



Experiment. Eggs Exposed. Membranes. 



June 26 14 



16 -I 



" 18 3 



.,20 35 



" 22 6O 



..24 78 



June 27 14 o 



16 -i 



" 18 3 



" 20 2O 



" 22 46 



24 56 



June 30 20 70 



22 93 



24 84 



July i 20 94 



22 78 



24 63 



July 25 20 48 



22 69 



24 94 



July 30 20 83 



22 87 



24 So 



1 2 l /2 M KCL gives closely similar results. 



This table shows, I think, that hypertonic sea-water alone will 

 induce membrane separation. In the most successful experiments 



