The Circulatory System of Lymnaea Stagnalis (L.)

Abstract

The present study deals with the circulatory system of the pulmonate freshwater snail Lymnaea stagnalis. As, due to structural and functional complications (e.g., open system, both lung and skin respiration), the study of circulation in gastropods is difficult, the present investigations had, in many respects, a preliminary character. Three methods for studying the blood system were used. Two of these (radiography and corrosion preparations) easily permitted to establish the main course of the vascular system in several areas of the snail. The third method (histological preparations of ink injected animals) was used for most of the investigations. The latter comprise the following subjects: the main arterial and venous systems of the whole animal, the nervous tissue, the skin of the head and the kidney-lung complex. Furthermore, details are given on several organs and tissues such as the buccal mass and the gizzard, the penis, the digestive gland and the ovotestis. The open blood system of L. stagnalis shows remarkable differentiations. Several organs (gizzard, buccal mass) are internally vascularized. Muscular contractions assist in circulating the blood through these organs. Other organs have a complicated external vascular system (nervous system, glands). Intraspecific and interspecific differences occur frequently in the circulatory systems of pulmonates. This is illustrated by a discussion of the vascular system of the central nervous system. The general circulation cannot be sustained by the action of the heart alone. Muscular contractions (during locomotion especially those of the columellar muscle) are indispensable. Hence the detailed circulation dynamics are difficult to establish. The provision of the tissues with oxygen occurs in complicated ways. This is connected with the fact that L. stagnalis has two systems of respiration, viz., skin and lung respiration. The vascularization of the kidney is distinctly of a type which may be expected in animals producing hypotonic urine. The system most probably lacks a counter-current principle. The details of the vascular system of several organs and tissues (e.g., kidney-lung system, central nervous system) roughly accord with those in other pulmonates. The description of the vascular system of the skin of L. stagnalis is new, and it is supposed that this system occurs generally in gastropods. For a further appreciation of the function and the dynamics of the circulation in pulmonates ecological and ethological aspects must be taken into consideration.