The Rhythmical Movements of the Gills of Nymphal Leptophlebia Marginata (Ephemeroptera) and the Currents Produced by Them in Water

1. The currents produced in water by the gills of the nymph of Leptophlebia are symmetrical with the body axis. The gills which lie at different angles with the body explore water above, at the sides and below the animal. 2. Each gill in movement shows a backward effective beat sharply defined from a forward recovery beat. In the latter the gill meets the water, edge forwards. In the former (effective) the gill moves through the water with its leading surface making an angle with its own path of motion. The forces involved are similar to those invoked for fish motion. 3. Each gill is a bilamellate structure, and a significant thing in water movement is the compression of water from between anterior and posterior lamellae during effective parts of an oscillation. 4. The symmetry of the current is related to the synchronous movements of members of pairs of gills. 5. After amputation of certain of the gills there appears to be no modification in the rhythmical movements of the remainder.