IMMUNITY AND SUSCEPTIBILITY OF SEA-URCHIN EGGS. 239 

 EXPERIMENTS WITH KC1. 



Experiment /., August 29, with NaCl, 15 pts. n to i of sea 

 water, exposure one hour, at chosen critical periods. Observa- 

 tion showed a slight rise in immunity from 70 to 95 per cent, up 

 to the beginning of segmentation, then a fall to 70 per cent, during 

 that process, but as opportunity for further experimentation was 

 lacking this result is hardly conclusive, though by itself it is con- 

 firmatory of the supposed greater immunity to NaCl than to KC1. 



Experiment /., with the Na citrate, August 13 ; 3 series, viz., 

 2 c.c. of seven-fourths ;/ Na citrate to 300, 400, 500 c.c. respec- 

 tively of sea water, diluted one half at transferral. 15' periods, 

 I hour exposure. Parallel observations showed that the eggs 

 so treated were ahead of control both in beginning to segment 



