rately. When the correct height of the drain pipe 

 is reached a few drops of water added to the 

 contents of the small vessel will be discharged 

 immediately. Setting the level of water in the 

 small vessel too low may lead to serious error as 

 the water will be forced through the gills by 

 gravity. Since readings may be grossly influenced 

 by poorly adjusted levels, repeated checking of 

 the overflow must be performed at regular and 

 frecjuent intervals. 



The rate of supply of sea water into the large 

 vessel should e.xceed the expected maximum rate 

 of water transport by the oyster, which rarely 

 exceeds 30 1. per hour. After equilibrium in the 

 water levels in the two communicating vessels has 

 been established , the tank is ready for use. Before 

 the oyster is placed in the tank the moUusk is 

 wrapped in thin rubber dam or in plastic sheeting 

 cut in the shape of an apron. This technique, 

 suggested first by Moore (1910), was adapted for 

 oyster research by Nelson (1936, 1938). A tri- 

 angular piece of sheeting cut to fit the shape and 

 size of the oyster is spread on a table. After the 

 valves are thoroughly scrubbed, washed, and 

 dried, the oyster is placed on its left valve on the 

 sheeting. The anterior half of the oyster is left 

 free; only the posterior half is wrapped in the 

 apron (fig. 168). The sheeting is attached to the 

 shell with melted colophonium cement, starting 

 with the lower (left) valve. Enough slack should 

 be left at the edges of the shell and at the hinge 

 side to allow free movement of the valve; small 

 cotton balls are inserted in both places to prevent 

 leakage of water. The two sides of the apron are 

 then brought together to make a sleeve of the 

 required diameter to fit the interconnecting trough 

 of the tank and are joined using hot colophonium 

 cement. A wide test tube is inserted in the apron 

 and the apron sleeve is sealed by pressing the two 

 sides of the apron against the glass while applying 

 the cement. Before the oyster is put in the tank 

 the apron should be tested against leakage by 

 gently blowing air into the sleeve. 



A small metal loop cut from the end of a paper 

 clip and cemented to the Ihxt valve is used to at- 

 tach a string leading to the kymograph lever, 

 which records the shell movements. The water 

 levels in the tanks are checked again; the oyster 

 is placed on a stand inside the tank and if necessary 

 immobilized by plastic clay; the sleeve of the apron 

 is drawn over the trough (or tubing) and is secured 

 by a piece of string; the writing lever of the kymo- 



graph is connected to the valve. The last ciieck 

 for a possible leakage of water is made after the 

 oyster opens its vah'es and begins to transport 

 water. The escape of water through the seams 

 of the apron can be detected by adding carmine 

 suspension and watching the currents. In a 

 correctly adjusted set all water transported by 

 the gills enters tiie small vessel through the sleeve 

 and can be collected, measured, and analyzed. 



The transport of water can be recorded con- 

 tinuously by using various automatic devices, such 

 as electric drop counters and dumping vessels. 

 The latter turn over after the water has reached a 

 certain predetermined level. Any of tliese devices 

 can be connected to tlie kymograph lever which 

 makes a mark on a rotating drum. The shell 

 movements and the temperature of water are 

 recorded sinmltaneously on the same sheet. The 

 arrangement of various parts of an apparatus for 

 recording the oyster activity and for collecting 

 samples of water before and after its passage 

 tlu'ough the gills is shown diagrammatically in 

 figure 169. The oyster in this diagran: has been 

 placed in a constant level tank A, whicli is provided 

 with two connecting vessels B and C A valve 

 l)etween A and B may be lowered to disconnect 

 tank A, and cap L is used to close the connection 

 between vessels B and C. Vessel B is slightly 

 larger than C and is used for taking samples of 

 water for plankton study or for gas analysis. The 

 water in this vessel is protected from direct contact 

 with air by the paraffined float H. The sample is 

 taken through the drain tul)e X. The small vessel 

 C has an overflow Y, which controls the levels of 

 water in all three vessels. From the overflow Y 

 water is delivered through tube Z to a dumping 

 vessel E, which is mounted on a horizontal axis. 

 A diagonal wall divides the vessel into two parts, 

 of wliich only one (facing the reader) is being filled 

 with water. Float F activates the system of 

 levers and releases the catch L which holds the 

 \essel in an upright position. The vessel over- 

 turns but snaps back into the position shown in 

 the diagram. Proper adjustment of the vessel is 

 obtained by attaching small weights (not shown 

 in the diagram) to its bottom. The vessel with 

 its levers is mounted on a solid frame D set on a 

 heavy concrete platform. The water discharged 

 at each dump activates the springboard G, which 

 is connected to a writing lever N. Shell move- 

 ments are recorded by tlie lever M; the electric 

 time sional S connected to a timer T records time 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



187 



