The postnatal development of the alimentary canal in the opossum. II. Stomach.

The postnatal development of the gastric mucosa in the opossum has been traced with the light, transmission and scanning electron microscopes. The formation of fovea and gastric glands occurs simultaneously during the postnatal period. During the first 60 postnatal days the developing gastric glands are composed of undifferentiated cells, parietal cells and scattered endocrine cells. Chief cells are not present until just before weaning (13 cm, i.e. ca. 75 days). Juvenile and adult animals show only a small population of chief cells, and these are confined to the bases of the gastric glands. The pH of stomach contents ranges from 6-0 to 6-5 until the time of appearance of solid food within the stomach, when it drops to 2-0-2-5. The surface cells lining the gastric lumen contain a considerable amount of what appears to be lipid during the first 3 weeks after birth, and this may indicate that the gastric mucosa is involved in the absorption of lipid during this period. The mode of lipid absorption appears to be different from that described for the intestinal tract of several other species.