Symmetry of heliotropic orientation in slugs

Abstract

The creeping of the slug Limax maximus shows no apparent neuromuscular asymmetry. But in heliotropic orientation there is chiefly involved the parietal musculature, where differential activity might conceivably be associated with the fundamental torsion of the body of the gasteropod. The point has been studied in relation to the occurence of “trial movements” at the beginning of the act of orientation, and has a special significance also for the analysis of “circus movements.” Experiment shows that a previously quiescent, dark-adapted Limax, illuminated from in front, turns with equal frequency to the right or to the left. Limax is negatively heliotropic, for all intensities used in these experiments. A similar equal frequency of turns to right and to left is found under non-stimulating (red) light. It would be incorrect to speak of these movements as “trial movements,” for in a series of 142 observations it was found that in 122 the direction of orientation coincided with that of the first indication of turning; only in 20 did the side definitively contracted differ from that first contracted (8 right; 12 left). Experiment shows that a previously quiescent, dark-adapted Limax, illuminated from in front, turns with equal frequency to the right or to the left. Limax is negatively heliotropic, for all intensities used in these experiments. A similar equal frequency of turns to right and to left is found under non-stimulating (red) light. It would be incorrect to speak of these movements as “trial movements,” for in a series of I42 observations it was found that in 122 the direction of orientation coincided with that of the first indication of turning; only in 20 did the side definitively contracted differ from that first contracted (8 right; 12 left).