The Water Relations of Snails and Slugs

Abstract

If H. pomatia are kept under conditions of constant temperature, humidity, illumination, food supply and water supply, their daily weight curves show great spontaneous fluctuations of an irregularly cyclical character, with a period of several days. Snails kept without food, but under otherwise identical conditions, show similar fluctuations of smaller amplitude (Fig. 1). A number of measurements of the oxygen consumption of H. pomatia were made at different points on the weight cycle. In fed animals, oxygen consumption tends to rise with weight. In fasting animals, the relationship between the two variables is less marked, and the oxygen consumption is always low (Figs. 2, 3). Aestivation tends to occur, even if environmental conditions are favourable, whenever the weight is low (Fig. 4). Feeding and digestion are apparently confined to the weight peaks, and incompatible with aestivation. The interrelations of internal and external factors in determining the activity level of H. pomatia are discussed. In drought, the activity outbursts are inhibited and the snail remains withdrawn, with low weight and oxygen consumption. Rain, after drought, releases the cycles again; the immediate mechanism of activation is not hydration of the tissues, but a stimulation effect.