Sensory systems involved in gravity orientation in the pulmonate snailLymnaea stagnalis

Summary

• 1. Effects of O₂ and of statocystectomy on gravity orientation ofLymnaea stagnalis were studied in a nearly isotropic light field.

• 2. In conformity with previous results O₂ affects the sign of gravity orientation and the orientation angle during geotactic behaviour (Fig. 2, Tables 1 and 2).

• 3. Statocystectomy experiments support the previously published hypothesis (Janse 1981) that peripheral interactions exist between O₂-receptors and statocysts (Fig. 2, Tables 1 and 2).

• 4. Without statocystsLymnaea can still orientate in the gravitational field. The sign of this type of orientation is affected by theP _O2 (especially of the lung contents), the orientation angle, however, is not (Fig. 2, Tables 1 and 2).

• 5. Apart from the statocystsLymnaea can also use the buoyancy of that part of the body which is contained in the shell for positive as well as for negative geotaxis (Fig. 3, Table 3). Indications were obtained that proprioperception plays a role in this type of (buoyancy) orientation.

• 6. Experiments in which the types of gravity orientation were artificially induced to counteract each other indicate that in water buoyancy orientation operates continuously but that the statocysts determine positive as well as negative geotaxis (Figs. 4 and 5, Tables 4 and 5).

• 7. Apart from the gravity orientation mechanism proper, O₂-conditions and statocysts also influence mechanisms which determine steering and creeping. The nature of these effects indicate that steering, creeping and the orientation angle during geotactic behaviour are induced by different neuronal mechanisms (Fig. 2, Tables 1 and 2).

• 8. Experiments in which geotaxis was studied at increasing time intervals after statocystectomy showed that the statocysts do not regenerate. Moreover, indications were obtained that as yet unknown internal factors also affect gravity orientation inL. stagnalis (Fig. 6).