Tracer studies of food absorption in the digestive tract of Nautilus pompilius (Cephalopoda, Tetrabranchiata)

In Nautilus pompilius, tracer experiments with C-14-labelled food show that the midgut gland, caecum and crop are involved in absorption of nutrients. According to liquid scintillation and light- and electron-microscopic auto radiography, the midgut gland exhibits the highest activity, followed by th e caecum and crop. The density of silver precipitates is highest in the ter minal alveoli of the midgut gland. Precipitates are also seen in the main c ells of the caecal epithelium. Few precipitates are found in the lamina epi thelialis mucosae of the crop, indicating that, in addition to food storage , digestive processes begin in this organ. These results have been confirme d by injection of the protein ferritin into the buccal cavity. The largest amount of ferritin is seen in the dense bodies of the main cells of the mid gut gland, whereas those of the main cells of the caecum and crop contain l ess ferritin.