by placing a small aquarium 25 x 13 inches over the top of the tank, 

 pouring 500 ml, of crude oil on the water of the aquarium, and treat- 

 ing the oil with carbonized sand. The depth of water was maintained 

 at two and three-fourths inches. Through an overflow the water from 

 this aquarium was delivered to the tank with oysters. The rate of flow 

 of water through each tank was maintained at the rate of three liters 

 per minute. The oysters used in the tests were four and five year old 

 marketable stock from private grovinds operated by a commercial company 

 in Narragansett Bay, Rhode Island. 



The results of the test were negative. Within the first three days 

 frcm two to six oysters died in each tank, undoubtedly due to weakness 

 frcm handling, but no further mortality occurred during the 35 days of 

 exposure in any of the tanks. The experiment was conducted in August 

 and September when the temperatvire fluctuated between 22<* and 18° C« 

 There was considerable accumulation of feces and pseudofeoes in all of 

 the tanks, indicating that oysters were feeding. At the end of the 

 test, a fairly good growth of shell, varying from one-eighth to one- 

 fourth of an Inoh, was noticed in many oysters* 



From these observations we conclude 'ttiat the 600 ml* of oil intro- 

 duced into a water system running at the rate of 180 liters per hour and 

 anchored by carbonized sand was insufficient to cause mortality or to 

 inhibit the growth of the shells of adult oysters* 



3* Effect of oil, oil extracts, and oils mixed with carbonized sand 

 on the rate of filtration of water t 



The maintenance of a steady flow of water through the gills of an 

 oyster is essential for its feeding and respiration. The current is 

 produced by the beating of the lateral cilia of the gills, while the 

 access of water to the branchial chambers is regulated by the position 

 of the opposing edges of the mantle and by ttie extent to which the shells 

 are open* Numerous small openings (ostia) on the surface of the gills 

 regulate the flow of water to the branchial tubes. Thus, the oyster has 

 several mechanisms by which the rate of flow of water may be controlled. 

 The ciliary epithellxxm may be compered to a pump, the capacity of which 

 depends on the rate of beating of the cilia, idiile the mantle and the 

 adductor miscle are comparable to a check valve which regulates the flow 

 of water* There is a certain degree of independence in the functioning 

 of the mantle and of the adductor muscle. The latter may be relaxed €uid 

 the valves of the oyster wide open while the. two edges of the mantle 

 come together and completely seal the entrance to the branchial cavity, 

 th-uB intercepting the access of water* 



The measurement of the rate of filtration of water is a very sensi- 

 tive means of studying the effect of changes in the envirorment of the 

 oyster, for the organism rapidly reacts to the presence of toxic sub- 

 stances which may be introduced into natural waters. Methods are available 



33 



