[Conditioned reflex to time in grape snails].

Tactile stimulation of the snail's mantle evokes unconditioned avoidance reflex of pneumostome closure. After 3--4 experimental sessions (10 stimuli per session, a session per day) of rhythmical stimulation (interstimulus intervals 1, 2, 4 min) with some stimuli missed, the pneumostome closure occurs at the time when the missed stimulus had to be delivered, i. e. expectancy learning takes place. Arhythmical stimulation does not produce such a result. When the stimulation is stopped only two or three conditioned responses are recorded.