Metachronal rhythms and gill movements of the nymph of caenis horaria (Ephemeroptera) in relation to water flow

Abstract

The nymph of Caenis by means of its gills produces a flow of water across its body from one side to the other. This flow is reversible. The transverse flow is related to the following phenomena. (1) Members of pairs of gills do not beat simultaneously so that across each pair a transverse rhythm is produced in line with the stream of water. (2) Each gill rises and falls, pivoting as it does so, and is inclined at an angle with its own path of motion. A single gill can produce a transverse flow in either direction by changes in its pivoting action, thereby changing the directional path of its leading surface. (3) The members of pairs of gills overlap, left over right in the case of a flow from right to left, but lie over each other in the opposite manner to this in the case of a flow from left to right. (4) Reversal of flow is associated with changes in (a) the method of pivoting of the gills, (b) their method of overlapping as members of pairs, (c) the direction of the transverse rhythm over the gills.