STRUCTURE OF THE DIGESTIVE-TRACT OF TORNARIA LARVA IN ENTEROPNEUSTA (HEMICHORDATA)

The ultrastructure of the digestive tract of tornaria larva of enterop neusts was investigated. It showed that the digestive tract consists o f three parts: esophagus, stomach, and intestine. The esophagus epithe lium consists of two types of multiciliated epithelial cells and solit ary muscle cells. Axonal tracts and neurons were found in the ventral wall of the esophagus. The cardiac sphincter contains an anterior band of strongly ciliated cells and a posterior band of cells with long va cuolized processes which partition the sphincter lumen. The stomach co nsists of three cell types: (1) cells with electron-opaque cytoplasm, bearing a fringed border on their apical sides; (2, 3) sparse cells wi th electron-light cytoplasm and different patterns of apical microvill i. Cells of the pyloric sphincter bear numerous cilia and almost no mi covilli. The intestine consists of three parts. The anterior part is f ormed of multiciliated cells which bear the fringed border. The middle part consists of flattened cells bearing rare cilia and vast numbers of mace-like microvilli. The posterior part of the intestine is formed of cells bearing numerous cilia and few microvilli. Muscle cells were not found in either stomach or intestine epithelium. One noticed that the structure of the digestive tract of enteropneust tornaria larva d iffers from that of echinoid pluteus larva.