The rate and retention of the habituation of the shadow reflex in Balanus improvisus (Cirripedia)

1. 1. There is large variation in the rate of habituation of the shadow reflex in the barnacle Balanus improvisus. This variation cannot be accounted for by the variation in the body size or in the activity of the animals. 2. 2. When only a short recovery time is allowed, the rate of the recovery of the habituated response is correlated with the rate of the preceding habituation. The same result is obtained when the habituation rate is varied using different animals or different temperatures. 3. 3. Habituation is more rapid at 12 °C than at 22 °C. 4. 4. Acetylcholine chloride (1·67 × 10 −5 g per ml) enhances the recovery of the habituated response. 5. 5. The results are in agreement with the transmitter depletion hypothesis of habituation.