At the beginning of each experiment, a fresh sample of oil and 

 sand was prepared and used without being renewed until the end of the 

 test# No oil slick was noticeable on the surface, but the water in 

 the oil-contaminated tank was slightly fluorescent in ultra-violet 

 light. No fluorescence was observed in the control tank. In a few 

 days after the beginning of each test, the oil and sand mixture became 

 covered with a layer of brown organic sediment which was not disturbed. 



The kymograph paper was changed once every day, always at 0800, 

 This moment was considered the beginning of each 24-hour period. Water 

 temperature was recorded two or three times a day. After being set and 

 adjusted, the constant level tanks and dumping vessels worked automatically 

 without serious mishaps. Only few records were lost because of the 

 failure of the dumping vessel to turn over or because of the stoppage of 

 the spring kymographs. 



Time was recorded at 30-minute intervals using a Telechrone eleotrio 

 motor. To the axis of this was mounted a plexiglass disc with two copper 

 springs set opposite each other at the periphery of the disc. In the 

 Icwermost position, the spring made contact with two terminals mounted 

 on a suitable base completing the electric circuit which activated small 

 signal magnets connected to writing levers. 



Di analyzing the records, the time of opening and closing of the 

 oyster and the number of dumps were summarized for each hour. The dump- 

 ing vessels were carefully calibrated before the experiments - their 

 capacity was 265 and 276 ml. The number of dumps per hour, recorded by 

 kymograph, was multiplied by the corresponding figure emd the maximum, 

 minimum, and the mean rate of pumping were computed. The mean rate of 

 pumping given in the tables refers to the periods the oj-^ter was open 

 and therefore considered as able to feed. By this method the efficiency 

 of the ciliary mechanisms can be more accurately expressed than by the 

 mean rate of pumping for every 24 hours, irrespective of whether the 

 oyster was open or closed. Thus, the figures of the mean rate of pump- 

 ing given in this report refer to the situations when the oysters had 

 an opportunity to filter water through their gills. The percentage of 

 time the oyster remained open each day is given in a separate col\imn. 



No attempt was made to control the temperature since it fluctuated 

 only within narrow margins not exceeding + 1,5° C. during a day. The 

 salinity of the water, as usual for Woods''Hole, remained fairly constsmt, 

 varying between 31 and 32 parts per thousand. 



In observing the condition of the sea water as it was running through 

 •tiie mixing chambers, it vreis noted that a fairly large number of copepods 

 accumulated in the last compartment of the chamber. On several occasions 

 the number of copepods was counted by using a magnifying glass and ex- 

 ploring the entire depth and width of the compartment. In the control. 



38 



