Ultrastructure of the reno-pericardial system in the pond snail Lymnaea stagnalis (L.).

Abstract

The ultrastructure of the organs involved in urine production in the pond snailLymnaea stagnalis is described. The atrial wall, which has been assumed to act as an ultrafilter, shows little ultrastructural correspondence with other ultrafilters, such as the mammalian glomerulus. Thus, ultrafiltration probably can take place in systems lacking the typical podocytes. The atrium of the stylommatophoreHelix pomatia appeared to differ only in quantitative aspects — it is thicker — from that of the basommatophoresL. stagnalis andBiomphalaria glabrata. The reno-pericardial duct consists of ciliated columnar cells, which contain considerable amounts of glycogen. The cells of the kidney sac are characterized by the presence of large (5–20 μ) excretion granules, which are constricted off together with part of the cytoplasm. In degenerating nephrocytes great numbers of lipid granules, probably arising from mitochondria, were found. Deposits of glycogen are present in the nephrocytes as well as in the cells of the ureter, suggesting the kidney to be a glycogen storing organ. The presence of glycogen is accompanied by that of an elaborate agranular endoplasmic reticulum. Although relative differences in the general ultrastructural pattern of the kidney sac and the ureter were found, some aspects of both epithelia—viz. the presence of numerous large mitochondria, a zone of microvilli at the free cell surface, and prominent infoldings of the basal and lateral cell membranes — suggest them to be involved in the reabsorption of solutes and in the transportation of ions and water.