METAMORPHIC CHANGES IN THE STOMACH OF THE FROG RANA-TEMPORARIA TADPOLES

The histological transformation of amphibian stomach during metamorpho sis was studied in the frog Rana temporaria. The earliest metamorphic changes occur shortly before regression of the cloacal piece of tail a nd appearance of forelegs. Autolysis of primary, larval epithelial cel ls and activity of phagocytes lead to regression of the apical mucosa, which is shed into the gastric lumen. Histogenesis takes place from t he very beginning of metamorphosis in the basal region of the mucosa; undifferentiated, regenerative cells, arranged in smalt compact cords and surrounded by a thick basement membrane, give rise to secondary li ning epithelium and glands. Lining epithelial cells differentiate into a typical mucosecretory epithelium. Oxyntic cells present in larval g lands are substituted by both ion- and protein-secreting oxyntic-pepti c cells. During metamorphosis, connective and muscular tissues markedl y increase, a submucosa, not present in larval tadpoles, gradually dev elops. A muscularis mucosae is also formed and the muscular propria be comes thicker. At late metamorphosis, folded structures involving both mucosa and submucosa develop, increasing the luminal surface as in ad ults. Removal of the larval gastric mucosa and its replacement by a ne w, adult-type definitive one, together with development of peripheral connective and muscular tissues, account for metamorphosis of tadpole stomach.