LARVAE OF ARBACIA PUNCTULATA 



371 



rapid decrease in size takes place. As concerns rate of growth, 

 the specimens in the experimental solutions behave similarly 

 to those in the sea-water to which NaOH had been added. 

 Solutions b, c, d and e produced -during the first 18 hours an 

 increasingly beneficial effect and g surpassed a by a smaller per- 



Figs. 71 to 74. Experiment 7. 



Fig. 71 7a, 24 hrs. Control. 



Fig. 72 76, figure 73 7c, figure 74 Id, 24 hrs. Solutions same as in the pre- 

 vious experiments. In this series the characters were more pronounced and the 

 irregularities very prominent at 24 hrs. 



Plot 10 



centage, indicating that the degree of alkaUnity most conducive 

 to growth at this period has been exceeded. 



At 18 hours, then, the concentration of solution e was opti- 

 mum for growth; at 24 hours, that of d; at 48 hours, that of c; 

 and at 72, that of a, as is indicated by their positions on the 

 growth-curves on the various days. Hence, although an in- 

 creased alkalinity produced an accelerated initial development, 



