I'O BULLETIN OF THE BUREAU OF FISHERIES 



DIRECT METHODS 



The first measurement of the rate of flow of water through the plankton-feeding 

 organisms was made by Parker (1914). Experimenting with the siliceous sponge 

 Stylotella, he adopted the following method: A glass tube was inserted into the oscu- 

 lum and the flow of water in the tube was determined by measuring the velocity of 

 floating particles, such as grains of carmine, that were carried up the tube by the 

 current. By placing the tube introduced into the osculum in a vertical position he 

 was able to observe the rise of water in the tube above the level of water in the tank 

 where the sponge was kept and thus measured the pressure produced by the ciliary 

 motion of the cells. 



A similar method was used by Allen (1914) in a study of the feeding habits of 

 fresh-water mussels. He introduced one end of the rubber tubing in the excurrent 

 siphon; the other end was connected to a calibrated glass tube having a capacity of 

 2 cubic centimeters between given marks. A neutral coloring matter was added into 

 the rubber tubing through a pipette thrust into it just outside the siphon and the 

 rate of flow of colored substance in the tube was measured. Because of the con- 

 traction of the siphon, Allen had considerable difficulty in measuring the velocity of 

 the outgoing current and made only one determination. Both Parker and Allen failed 

 to note that the velocity of the current running in a circular pipe varies along the 

 cross section of the pipe, the maximum velocity being at the center, with minimum 

 velocity close to its walls. Consequently, no discharge of water can be computed 

 from their data unless the position of the particle, the speed of which is being measured, 

 is known. When the carmine grains flow in water they settle on the bottom gradu- 

 ally and are carried out at different speeds depending on the distance from the center 

 of the tube. 



METHODS EMPLOYED IN THE PRESENT INVESTIGATION 



Two methods of measuring the rate of flow produced by the gills of the oyster 

 were described by the author in 1926 (Galtsoft", 1926). It is desirable to give a more 

 complete description of them here. 



TANK METHOD 



This method is designed primarily to collect the water after it had passed through 

 the gills and to measure the pressure inside the gill cavity. The valves of the oyster 

 are forced apart and a glass rod is placed between them to prevent their closing; a 

 rubber tube 6 to 7 millimeters in diameter is inserted in the gill cavity and made 

 fast by packing all the spaces around with cotton. The outgoing water passes through 

 the tube; leakage, if any, can be noticed easily by adding a few drops of carmine 

 suspension and watching the produced currents. The oyster is then placed in a 

 tank (fig. 2) of about 10 liters capacity; the tank is connected through a horizontal 

 glass tube (b) of 6 miUimeters diameter, with a small vessel (v) of about 50 centi- 

 meters capacity. A vertical tube (c), 8 millimeters in diameter, passes through 

 the bottom of a small vessel and serves as an overflow; its upper level is about 1 

 centimeter above the upper level of the horizontal tube b. The tank is made of 

 celluloid, J/g inch thick; the walls are cemented with a solution of celluloid in acetone. 



