INTRODUCTIONWork on pumping and filtration rates of bivalve molluscs was initially concerned with the physiological concept of pumping water through the mantle cavity. Comprehensive reviews are given by Winter (1970) and Ali (1971). The methods are of two kinds; direct, in which the flow of exhaled water itself is measured, and indirect, in which the rate of clearance of food particles is used to calculate water flow through the gills.There is a disadvantage in the indirect method when used to calculate volumes of water pumped because it involves the assumption that a fixed percentage (often 100% with large particles) of the particulate matter passing through the gill system is retained. Pumping rate is thus estimated as a function of the particle collecting properties of the latero-frontal cirri, whereas the water current is produced by the lateral cilia. Although the structure of the latero-frontal cirri is now well documented (Moore, 1971), their efficiency in particle retention can alter under certain conditions (Dral, 1967). There is need, therefore, for direct measurement of the quantity of water pumped. Recent advances in the understanding of branchial innervation and the control of lateral ciliary activity also reinforce this point (Aiello, 1960, 1962, 1970; Paparo, 1972, 1973).The constant level chamber for direct measurement of pumping rate was devised by Galtsoff (1926), to ensure that separation of the exhalant water current from the bivalve was not interfered with by pressure differences produced by the process of separation. The apparatus has been used in various forms by Galtsoff (1926, 1928, 1946), Nelson (1935, 1936), Collier & Ray (1948), Loosanoff & Engle (1947), Loosanoff & Nomejko (1946) and more recently by Drinnan (1964) and Davids (1964).
Glacial lake drainage: a stability analysis
