Fig. 1. Apparatus and procedure used in odor-aversion conditioning. (A) A view of a slug's head and tentacles. (B) The experimental apparatus. Concentric circles with radii of 45 mm and 15 mm were drawn on black paper, and a glass plate was superimposed on the paper. This was lit from above. (C) Procedure for odor-aversion conditioning. (i) Carrot juice (1 ml) was laid on the glass plate in the shape of the larger circle with a radius of 45 mm. A slug was placed on the center of the circle. (ii) In the paired conditioning, 1 ml of quinidine sulfate solution was applied to the mouth of the slug when it was just about to touch the carrot juice.