Histological changes in Xenopus laevis Daudin adult specimens kept under dry conditions, then moved back to their natural aquatic environment. II. Skin, kidney and interrenal tissue.

Some cytological and histochemical characteristics of skin, the kidney and interrenal tissue were studied in Xenopus laevis adult specimens (1) kept in their natural aquatic environment; (2) gradually exposed to dry conditions under which they were kept one week; and (3) returned from the dry environment to water for 24 hr or a week. In the skin, the most relevant changes are those exhibited by epidermal "flask" cells. These cells are generally rather lean, tall and PAS-positive in "dry" animals and in those 24 hr after replacement in water, whereas in animals placed back in water for a week "flask" cells are often large and faintly stainable. In "dry" animals, the skin mucous glands look more emptied of secretion granules than in control animals kept in water or in "dry" specimens returned to water. Difference in the epidermis thickness or in its histochemically evidenced alkaline phosphatase activity were not observed between different groups. In the kidney a clearcut difference between animal groups was found in the glycogen content of the proximal convoluted tubules of the nephron. Glycogen level is very low in "dry" animals. These variations are tentatively ascribed to different degrees of electrolyte resorption. In the interrenal cells, the sudanophil material is scanty in "dry" animals, while it is much more abundant in those returned to water for 24 hr. Similar, though less pronounced, effects had been obtained in previous experiments of ours, in which some of the animals were kept out of water on moist moss, that is under less severe conditions of water deficiency than in the present experiments.