1. A pulmonate land snail, Fruticicola (Acusta) sieboldiana (Pfeiffer), which is a pest of vegetables in Japan, scarcely shows daily rhythmic activity in its younger stage, but as it grows the activity becomes more and more rhythmic, and when the shell grows up over 0.9 cm. in height it shows typical daily rhythmic activity. 2. The activity is significantly affected by humidity. When the relative humidity is below 70%, the animal remains motionless. But when the relative humidity exceeds 90% and the animal is maintained in darkness, it begins to move about even when the peristome is covered with a white film (epiphragm).

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