The Fate of Thorium Dioxide Injected into the Pedal Sinus of Bullia (Gastropoda: Prosobranchiata)

Abstract

1. The removal and ultimate disposal of foreign particles injected into the haemolymph of the sandy-beach snail, Bullia, has been studied by using the radio-opaque dye Thorotrast. 2. Particles are removed by phagocytic haemocytes which migrate by various routes to the outside of the body. The main pathway is through the heart wall into the pericardial cavity and via the renopericardial canal into the lumen of the kidney, from which the cells escape into the mantle cavity. 3. The injection of foreign particles stimulates a marked increase in the haemocyte population and also in the mitotic index. 4. The final discussion integrates the available evidence and a comparison is made between Bullia and other molluscs. The origin of the macrophages is discussed.