Sorting and Retention Time of Particles in the Digestive System of Lymnaea Stagnalis (L.)

Abstract

In the present study sorting, retention time and rate of transport of food and of non-food particles in the digestive system of Lymnaea stagnalis was studied, using X-ray opaque markers with different particle size (Thorotrast, Microbar and Barotrast) and X-radiography. With these techniques it was possible to compose a diagram showing the various regions of the digestive system as located in situ in the snail. The gross morphology corresponds to that of Lymnaea stagnalis appressa Say. From experiments on food consumption and from measurements of the digestive gland fractions in the faeces it was concluded that, under the experimental conditions, the food consumption as well as the activity of the digestive gland were alike in the light and in the dark. The sorting of particles in the digestive tract, which is mainly accomplished in the pylorus, is responsible for the three fractions distinguishable in the faeces. Coarse materials are transported directly from the gizzard to the intestine (gizzard string). Small particles such as chloroplasts (4 × 6), Thorotrast and Microbar (particles 0 0.1-0.4), and Barotrast (particles 0 1.0-10.0) are transported to the junction of the digestive gland ducts and the pylorus. It is supposed that only particles with a distinct maximum diameter (up to 0.4), which are suspended separately in the fluid in the pylorus will be passed into the digestive gland. Material from the digestive gland is transported from the digestive gland ducts to the intestine (digestive gland fraction), and this fraction forms clear-cut intersections in the gizzard string. Particles with a diameter over 0.4y are transported from the junction of the digestive gland ducts and the pylorus to the intestine by way of the caecum (caecal string). This fraction is a thin string running alongside or twisting through the two others. The different treatment by the sorting mechanism of the particles of Microbar and Thorotrast, which have about the same diameter is discussed. Radiographs showed X-ray opaque marker to be present in the caecum already 5 min after feeding the marker. The first faeces containing the ingested markers were deposited approximately 4 hrs after feeding. The rate of transport through the digestive tract was calculated as about 10 mm per hr. Experiments with Thorotrast, which entered the digestive gland, demonstrated that this marker was present in the digestive gland during about 4 days after the administration. From these data and from measurements of the digestive gland fractions of the faeces it was concluded that the digestive processes of the cells in the digestive gland are not synchronized.