Histological and histochemical studies on the digestive system of Squilla oratoria

The digestive system of Squilla oratoria De Heart was studied by histological and histoche mical methods .The digestive system includes digestive tract and hepatopancreas .The former consists of mouth, esophagus, stomach(cardiac stomach and phloric stomach), midgut and midgut caecum ,hindgut and anus .The hepatopancreas is well developed .It is a multitubular gland .The tubular epithelium consists of secretory cells, storage cells ,absorptive cells and a mbryonic cells. There is an obvious secretory vesicle in the apical region of secretory cells .The cells show activity of proteinase ,non-specific esterase and lipase .They may secrete the enzy mes into tubular In mina by exocytosis of the secretory vesicles or disintegration of the apical region of the cells. The enzymes are transported into digestive tract and play a role in the extracellular digestion.The absorptive cells are rich in RNA and protein, which shows that the cells can synthesize protein actively. The storage cells contain lipid and glycogen, and show alkaline phosphatase activity in the basal plasma me mbrane .The results show that the cells can transport nutritive materials into blood space among tubules .The a mbryonic cells are s mall·The cytoplas ms are basophilic and the nuclei are large. The mucosa epithelium of the digestive tract consists mainly of columnar cells.The epithelial surface of the stomach is covered by cuticle.The cardiac stomach has well-developed muscular layer.It may grind food mechanically. The cuticle in the phloric stomach is specialized into infra ampullary ridge and supra ampullary ridge which can filter food.The epithelial surface of the midgut is covered by no cuticle. The epithelial cells show activity of proteinase, non-specific esterase and 1iPase, which shows that the midgut may also secrete digestive enzymes. The microvilli in the epithelial cells indicates the midgut may absorb food .The lumen of the hindgut is large, while the epithelial cells show weak activity of non-specific esterase and no activity of proteinase and lipase .So the hindgut may play a role only in storage and excretion of faces .The esophageal gland locates in submucosa of the esophagus .The gland cells which are pyramidal in shape secrete acid mucopoly saccharides.