PROGRESS IN BIOLOGICAL INQUIRIES, 191^9 1117 



Phenomenon of nettiny. — A study of tlw; physiology of the (jyster 

 l.iivse was continued by H. F. Prytlier(;h at Milford, Conn. It was 

 discovered in 192.S that c(^pper salts would produce settin<j: of a fully 

 developed oyster larva, or in other woi'ds, cause it to <ro throu<^h 

 tlic processes necessai-y for its attachment and metamorphosis. By 

 u>iu^ extremely minute quantities of this metal, it was possible to 

 obtain for the first time detailed observations and photoj^raphs of 

 this important sta<2:e in the life history of the oyster. 



The setting of the larva is a biological reaction of a most positive 

 character, which occurs in nature under rather definite physical 

 conditions. In Milford Harbor, setting was observed to occur during 

 the period of low slack water, which differs from all other stages of 

 tide in that the salinity and hydrogen-ion concentration of the water 

 are lowest and the temperature highest. In other words, setting 

 occurs at a stage of tide when the effect of river discharge is greatest 

 on the physical condition of the water over the oyster beds. By 

 experiments carried out during the past two summers, it was found 

 that changes in salinity, temperature, oxygen content, and hydrogen- 

 ion concentration would not produce tlie setting of the larva in a 

 single instance. However, when the salinity was reduced by the 

 addition of river water instead of distilled water, setting took 

 place, which indicated that either some substance or physico-chemical 

 change introduced by river water was responsible for the producing 

 of the setting reaction. 



A series of experiments was then undertaken to test the effect of 

 the various chemicals occurring in river water on the setting of the 

 larva. Various concentrations of the chlorides, carbonates, and sul- 

 phates of sodium, potassium, calcium, and magnesium gave nega- 

 tive results, as did also sodium nitrate and nitrite and compounds 

 of aluminum, lead, zinc, tin, silver, and iron. The only substance 

 tliat gave a positive setting reaction was copper in the form of a 

 pure metal or as a carbonate, sulphate, or chloride. Concentrations 

 of 1 part copper to 500,000 or 1,000,000 parts of water were sufficient 

 to j)roduce setting and initiate almost immediately the beginning 

 of the attachment process. 



In river water, copper occurs in extremely small amounts and 

 at periods of low slack water there are undoubtedly enough free 

 metal ions to stimulate the larva and cause setting. In water of low 

 salinity (16 per mille) the process of setting required 15 to 30 

 minutes; while in salinites of 25 to 28 per mille, the larva seemed 

 to experience considerable difficulty in secreting the byssus and 

 cementing fluid and did not become attached for 2 or more hours 

 after exposure to copper ions. This phase of the setting problem 

 will be taken up in greater detail during the coming summer. 



The studies thus far show quite conclusively that the copper 

 brought down by the river may become a factor which controls the 

 time and place of attachment of oysters. 



SLRM5YS OF OYSTER BOTTOMS 



Alahama.—ln April. 1929, at the request of I. T. Quinn, Alabama 

 State Conservation Commission, Dr. Paul. S. Galtsoff made 

 a survey of the oyster bottoms with the view of determining the 



