1. 1. About 400 limpets were observed in June and July 1967 and 1968 at Saye Bay, Alderney, in the Channel Islands, in order to study their homing behaviour. 2. 2. Movements of limpets were recorded using triangulation and photography. Homing was a regular feature of the behaviour of these limpets at all times and states of tide. 3. 3. The movements of P. vulgata are governed by a timing sense by which they consistently return home before being covered by the tide. 4. 4. The limpets did not use celestial information to navigate home, since they are capable of homing at any time of day, and in any weather, and even when the rock is reorientated. It is, therefore, concluded that the information available for homing is restricted to the rock and the past movements of the limpets. 5. 5. Displacement experiments were conducted, the results from which were inconsistent with the idea of a kinaesthetic memory. 6. 6. Experiments in which trails were damaged by rock chipping and by scrubbing with detergent failed to prevent homing. Limpets were also able to home after forced detours resulting from obstruction on their homeward trails. These results cast doubt on topographic memory and simple chemical trail-following as homing cues. Later experiments in which the rock surface was cleaned chemically gave inconclusive results, as homing ability was not significantly lowered. 7. 7. Recognition of scars by limpets other than the occupant is demonstrated, and it is postulated that orientated chemical labelling is necessary. 8. 8. Chemical hypotheses of homing, scar recognition, and orientation on to the scar are proposed and discussed. © 1969.
