1918 



Hall; on Sea-urchin Eggs 



117 



of Q.65, all eggs subjected to the acid before cleavage began, were badly 

 inhibited, the 16-celled stage being the limit of growth. Those put in 

 while from 1 — 8-celled became abnormal at the blastula stage; those 

 from 32-celled to the blastula formed abnormal gastrulae. With a pH 

 of 6.7 — 7.05, those put in 30 minutes after fertilization developed only 

 to the 8-celled stage ; all others formed blastulae or abnormal gastrulae. 

 Using a pH of 7.25, eggs fertilized for two hours but with no cleavage, 

 formed normal blastulae ; blastulae and gastrulae developed normally. 

 Similar results were obtained with a pH of 7.6 — 8.0. 



In the third type of experiment fertilized eggs at different stages 

 of development were put into H2SO3 for 4 — 6 hours, then returned to 

 sea- water for further growth (table 4). This method seemed to cause 

 fewer abnormalities than either of the other experiments. In a pH of 

 Q.5, 2-celled eggs in acid for 4 hours developed normally, 8-celled to 

 blastula stages in acid for 6 hours developed normal blastulae and gas- 

 trulae. In a pH of 6.65, blastulae in the acid for 6 hours formed normal 

 gastrulae. Gastrulae put into acid for 6 hours continued to develop 

 normally after return to sea-water. 



Table 4. Effects of exposure to HoSO^ for 4 — 6 hours 



When testing the adult sea-urchins, one large and one small individual 

 were used in each concentration. With a pH of 6.1 both animals lived 

 for 1 day and 21 hours. The acid water was kept running the first day 

 but was unchanged during the second. It was clear and free from odor 

 at the end. In the second jar, with a pH of 6.85, the small one died in 

 20 hours and the large one in 1 day and 20 hours. The water was 

 murky and foul-smelling, however. This would seem to indicate a germi- 

 cidal effect in the stronger solution. In the experiments with medusae 

 four concentrations of acid were used, with pH of 6.75, 7.45, 7.6, and 7.8. 

 The water was changed frequently to keep the pH constant. Thaumantias 

 cellularia was more active in all concentrations at first, but died in 23 



