LARVAE OF ARBACIA PUNCTULATA 



385 



The individuals in this experiment were considerably larger 

 than those of the general average for the corresponding period 

 of that summer. The specimens in solution b exceeded in 

 size those in a during the entire period; those in c and d, al- 

 though smaller at the age of 24 hours, grew more rapidly and 

 when 120 hours old, were larger than those of the control. Those 

 in e underwent an initial inhibition, but at the age of 96 hours 

 they attained almost as great a size as those in a; but failed to 

 live through the following day. 



If the production of the specific effects of the carbonate 

 is due to the fact that molecular MgCOs and CaCOs are pushed 



Plot 13 



nearer to the point of saturation and rendered more available 

 for the use of the embryo, then dilution of sea-water with NaCl 

 should produce modifications consistent with a less saturated 

 condition; and this is what actually occurs. The skeletons are 

 more slender than in the normal individual, and are charac- 

 terized by conspicuous perforations in the lattice-work of the 

 arms, and thorn-like spines and processes of the body-rods. 



Since the alkalinity of the sea-water is reduced by dilution 

 with neutral NaCl solution, we might expect a reduction in 

 size; but, on the contrary, an increase above the normal occurs — 

 in Experiment 14 even at 30 per cent dilution. But it is sig- 

 nificant that in solutions c and d, in which the specimens ulti- 

 mately attained a greater maximum growth than did those in 

 a, an inhibition was produced during the first day, the time 



