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Puget Sound Marine Sta. Pub. 



Vol. 1, No. 14. 



caused cessation of development in the eggs of a European sea urchin. 

 Slight increase in alkalinity causes an increase in growth and cell divi- 

 sion, while very small additions of acid inhibited these processes. Whit- 

 ley (28) found further that the same relations obtained in the case of the 

 developing eggs of plaice. It is difficult to say how much the addition 

 of alkali and acid modified the concentration of hydrogen and hj^droxyl 

 ions in the case of the experiments of these investigators or my own, 

 because the determination on ion concentration requires special methods. 



Table 6. Showing comparative resistance of echinoderms, mollusks and 

 barnacles from different depths, to fresh xcater. 



♦Several additional experiments performed, part with similar results and 

 part with a view to determine an exposure which would be likely to give 

 differential results. 



