The ontongeny of the stomach in the pouch young of the Red Kangaroo

Abstract

The anterior four-fifths of the stomach of the red kangaroo consists of a sacculated region, the mucosa of which is made up of cardiac glands. This mucosa elaborates no intrinsic digestive enzymes but the stomach contents contain amylase, probably of bacterial origin. The cardia leads into a gastric pouch lined by fundic tissue composed of parietal and chief cells. The pH of this region is acid and extracts of the mucosa have peptic activity. The gastric pouch communicates posteriorly with a pyloric region. The stomach is elongated and is coiled spirally on itself, the inside of the spiral being modified to form a groove lined by stratified cornified epithelium. The stomach of the neonatus exhibits this spiral arrangement. The whole of the stomach, however, possesses peptic activity due to the secretion, by cells of one type only, of acid and pepsin. This cell type exhibits the characteristics both of parietal and chief cells judged with the electron microscope. It is thus analogous to the bipotent cell in the stomach mucosa of frogs. At about the 200th day of pouch life the epithelium of the anterior four-fifths of the stomach is transformed into cardiac glands, and in the posterior one-fifth a gastric pouch is formed which contains differentiated parietal and chief cells. At the 236th day the definitive structure of the adult stomach is achieved and all peptic activity is confined to the posterior gastric pouch region.