IN a recently completed series of laboratory studies, lebensspuren were produced by individual macrobenthic organisms on a variety of marine sand and mud substrates (freshly collected from depths down to 30 m in the Bristol Channel), from which all other macrofauna had been removed by passing it through a 1.0 mm mesh. But the resultant tracks, trails and burrows gradually disappeared when the aquarium tanks containing them were left undisturbed after the termination of the experiments.