308 The Influence of Environment 



The concentration of the NaCl in the sea water at 

 Woods Hole (where these experiments were made) 

 is about m/2, and as soon as this concentration of NaCl 

 is reached the eggs are all killed as a rule before they 

 can form an embryo, unless a small but definite amount 

 of Ca is added. It was found that the eggs can be 

 raised in much higher concentrations of NaCl, but in 

 that case more Ca must be added. The following 

 table gives the minimal amount of CaCl 2 which must 

 be added in order to allow fifty per cent, of the eggs 

 to form embryos. (The eggs were put into the solu- 

 tion an hour or two after fertilization.) 



TABLE XVI 



This indicates that the quantity of CaCl 2 required 

 to counteract the injurious effects of a pure solution 

 of NaCl increases approximately in proportion to the 



