The Influence of Environment 311 



eggs of the sea urchin? Before we answer this ques- 

 tion, we wish to enter upon the discussion of the nature 

 of the injurious action of a pure NaCl solution of a 

 certain concentration and of the annihilation of this 

 action by the addition of a small quantity of Ca. The 

 writer suggested in 1905 that the injurious action of a 

 pure NaCl solution consisted in rendering the membrane 

 of the egg permeable for NaCl, whereby the germ 

 inside the membrane is killed; while the addition of a 

 small amount of Ca (or any other bivalent metal) 

 prevents the diffusion of Na into the egg, ' possibly, as 

 T. B. Robertson =* suggested, by forming a precipitate 

 with some constituent of the membrane, w^hereby the 

 latter becomes more impermeable. The correctness 

 of this idea can be demonstrated in the following way. 

 When eggs of Funduhis, which are three or four days 

 old and contain an embryo, are put into a test-tube 

 containing 3 m NaCl they will float on this solution for 

 about three or four hours ; after that they will sink to 

 the bottom. Before this happens the egg will shrink 

 and when it ceases to float the embryo is usually dead. 

 This is intelligible on the assumption that the NaCl 

 solution entered the egg, increased its specific gravity 

 so that it could not float any longer and killed the 

 embryo. When w^e add, however, i c. c. 10/8 m 

 CaCU to 50 c.c. 3 m NaCl the eggs will float, the 



* Loeb, J., Arch. f. d. ges. Physiol., 1905, evil., 252. 



* Robertson, T. B., Ergeh. d. Physiol., 1910, x., 216. 



