128 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



7. The different selective preferences exercised are explained by the past history 

 of the sea-water environment. Magnesia and sodium steadily increased, but lime and 

 potassium must have reached their present proportions ages ago; and the internal 

 epithelial cells of medusae accommodated themselves accordingly, although they have 

 not yet accommodated themselves to the increasing sodium and magnesia. 



8. The inorganic composition of medusae, as shown by Professor Macallum's re- 

 searches, reflects the composition of sea-water less of to-day, than of past geological 

 periods, possibly very remote periods. 



