Quarterly Journal of Microscopical Science, Vol s3-88, 15-25, Copyright © 1947 by Company of Biologists

The Nephridia of Geonemertes Dendyi

¹ Zoological Laboratory, Cambridge

1. The nephridia of the terrestrial nemertine Geonemertes dendyi are described. The flame-cells are in groups, each of which communicates with the exterior by its own duct. The flame-cells open into the branches of a ciliated end-canal. Distally this end-canal executes a number of convolutions and then passes into a non-ciliated glandular canal. The first part of the glandular canal is also convoluted, and the distal part of it passes to the efferent duct.

2. The nephridia are distributed over most of the surface of the animal immediately below the muscular layer. The convolutions of the end-canals and glandular canals lie somewhat deeper, in well-defined lacunae in the parenchyma.

3. Evidence is presented that fluid can be excreted into the nephridia. The activity of the flame-cells varies with the degree of hydration of the animal and may cease on desiccation. The flame-cells can be stimulated to activity by dilution of the body fluid of crushed animals with tap-water. The relation of water excretion to the mechanical activity of the flame-cells is discussed.

4. Some features of the natural habitat and the water relations of the animal under natural conditions are described. It is pointed out that the animal may have to contend not only with desiccation but with excessive hydration. The physiological consequences of hydration appear to be met by the flame-cell mechanism.