Fig. 6. Apparatus and procedure of odor-aversion conditioning with a shading box. (A) The experimental apparatus with a shading box. (B) During the conditioning, 1 ml of carrot juice was laid in the shape of a half circle with a radius of 60 mm. (C) The conditioning procedure. (i) The slugs were placed just behind the center of the start line. (ii) For the slugs in the paired conditioned group, 1 ml of saturated (approximately 1% w/v) quinidine sulfate solution was applied to the mouth of the slug when it was just about to touch the carrot juice. At the same time, we recorded the time it took to reach the carrot juice after the middle of the slug's body passed the start line. If the slug did not reach the carrot juice within 3 min, it was eliminated from the experiments. (D) In the retention test, the carrot juice was laid in the shape of a half circle with a radius of 90 mm, and we tested whether they avoided the carrot juice for at least 3 min.