Abstract
Hensen (,1887) drew attention to the possibility of using a pump for quantitative sampling of surface plankton and, since then, a hose-pump method has been widely used for such sampling at desired depths by Juday (1916), Lohmann (1898,1901), and Thorson (1946). A comparative study by Gibbons & Fraser (1937) suggested that such a pump had outstanding advantages over the vertical net, in quantitative work. However, Korringa (1941), working on oyster larvae, suggested that some plankton animals may be able to escape by swimming against the currents which approach the mouth of the suction hose. Brook & Woodward (1956) noticed an apparently rheotactic response shown by plankton organisms in evading water currents.