118 Pub. Piiget Sound. Biol. Sta. Vol. 2, No. 40 



hours in all. Phialidium gregarium showed no pulsations in the 6.75, the 

 only sign of life being a closing of the bell when stimulated. These in 

 a pH of 6.75, died in 24 hours. Those in the other concentrations lived 

 3 hours longer but showed only occasional or very slow pulsations during 

 the last 10 hours. 



SUMMARY AND DISCUSSION 



Unfertilized eggs exposed to H2SO3 of N/7500 or weaker for a period 

 not longer than 1^ hours develop normally when fertilized either in acid 

 or in sea-water. 



Eggs in different stages of development exposed to HgSOg of N/7500 

 or weaker, develop normally. 



Eggs exposed at different stages of development for 4 — 6 hours, or 

 a tide period, to strengths from N/1800 to N/2300, were not injured 

 but developed normally, 



Altho death does not occur immediately in solutions stronger than 

 N/7500, still abnormalities appear sooner or later which prevent the 

 formation of normal adults. This condition would be as fatal to the life 

 of the species as death. In the Miles Acid Process strengths over N/10000 

 would probably never be reached, and even greater dilutions would be 

 probable since sulphur dioxide passes off rapidly. It seems then that 

 the sea-urchin would be able to live in the waters which receive sewage 

 treated in this manner. Since the sea-urchin normally lives on clean 

 rocky bottom free from contamination it is probably more sensitive than 

 the clam and oyster which live in similar depths, but where the pH is 

 more variable and where there is liable to be more contamination. The 

 sea-urchin may be considered as an index organism for these forms. 

 We may predict therefore that the shellfish would not be destroyed by 

 this process when sulphurous acid or sulphur dioxide is used. 



I wish to thank Dr. V. E. Shelford, at whose suggestion this work 

 was undertaken, for his interest and helpful suggestions. I am indebted 

 to Dr. J. F. Bovard and Dr. C. M. Child for their assistance with the 

 embryological work. 



