1. The weight of active specimens of Helix pomatia L. undergoes continual fluctuation, the changes from day to day being often of very great magnitude and presenting the appearance of an irregular rhythm.

2. The animals tend to aestivate at the times when their weight is low.

3. The weight fluctuations are not responses to varying environmental conditions.

4. The weight fluctuations are seen in animals given water but no food, and are not seen in those given food but no water. They are therefore due primarily to variations in the water content of the animals.

5. The amplitude of the fluctuations is greater in fed than in fasting animals.

6. Similar fluctuations, but of somewhat smaller amplitude, occur in snails kept in air saturated with water vapour.

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