316 The Influence of Environment 



out how much CaCl s , was required to allow them to 

 swim permanently at the surface. 



TABLE XIX 



C.c. of m/16 CaCh Neces- 

 sary to Induce the Ma- 

 jority of the Larva to 

 Swim in 



50 cc. NaCl+KCl+0.75 

 50 c.c. NaCl+KCl+ 1.5 

 50C.C. NaCl+KCl+ 2.5 

 50 c.c. NaCl+KCl+ 5.0 

 50 c.c. NaCl+KCl+10.0 

 50 c.c. NaCl+KCl+15.0 

 50 c.c. NaCl+KCl+20.0 



c.c. 3/8 m MgClz 

 c.c. 3/8 m MgCl 2 

 c.c. 3/8 m MgCl 2 

 c.c. 3/8 m MgCl 2 

 c.c. 3/8 m MgCl 2 

 c.c. 3/8 m MgCl 2 

 c.c. 3/8 m MgCl 2 



In order to interpret these figures correctly we must 

 remember that we are dealing with two different an- 

 tagonisms, one between the salts with univalent and 

 bivalent metals and the other between Mg and Ca. 

 The former antagonism is satisfied by the addition of 

 Mg, inasmuch as enough Mg was present for this 

 purpose in all solutions. What was lacking was the 

 balance between Mg and Ca. The experiments in 

 Table XIX therefore answer the question of the ratio 

 between Mg and Ca. If we consider only the concen- 

 trations of Mg between 2.5 and 10.0 c. c. y % m MgCl 2 

 — which are those closest to the normal concentration 

 of Mg in the sea water — we notice that CQa must 

 vary in proportion to CMg. If we now combine the 

 results of this and the previous paragraph we may 



