LARVAE OF ARBACIA PUNCTULATA 



359 



On June 15 of the succeeding year the second experiment was 

 begun and solutions of the following composition employed: 



Experiment 5. Plot 8. June 15, 1915 



a Sea-water 



h 99.75 cc. S. W. + 0.25 cc. N/10 Acetic acid 



c -. 99.50 cc. S. W. + 0.50 cc. N/10 Acetic acid 



d 99.25 cc. S. W. + 0.75 cc. N/10 Acetic acid 



e 99.0 cc. S. W. + 1.00 cc. N/10 Acetic acid 



/ 98.75 cc. S. W. + 1,25 cc. N/10 Acetic acid 



g 98.50 cc. S. W. + 1.50 cc. N/10 Acetic acid 



The growth curve for the control in Experiment 4 indicates a 

 size somewhat larger than that of the general average of the 

 controls for that season. Compared with the control of Experi- 

 ment 5, it measures somewhat more at the ages of 24 and 48 

 hours; then undergoes an inhibition of growth, resulting in a 

 size at the age of 120 hours but little larger than the average of 

 5a at the age of 72. 



Only three of the cultures that were treated with acids in 

 Experiment 5 formed skeletons; in 5e the eggs segmented and 

 finally reached an early gastrula stage, but were abnormal and 

 did not swim at the surface. In h, c and d there was an extremely 

 rapid development following a slow growth during the first few 



