CUTANEOUS ADAPTATIONS TO WATER-BALANCE IN AMPHIBIANS

1. The integument of the amphibians is, in general terms, not adapted to a strictly terrestrial life, in that it does not serve as a barrier to a bidirectional water flow. 2. One of the major problems which thu s faces the terrestrial amphibians is dehydration. 3. To reduce water loss, or to absorb water through the skin, some amphibians have develo ped morphological and behavioural adaptations capable of acting togeth er to maintain the hydric balance. 4. Skin texture and sculpturing see m to be involved with water absorption. A granular ventral skin absorb s more efficiently than a smooth skin; the occurrence of cutaneous gro oves in the ventral and lateral regions of the body in the salamander and the bufonids permits the transfer of water to other parts of the b ody by capillarity. 5. The arrangement of the superficial epidermal ce lls, sometimes united, sometimes separated by ample intercellular spac es, and also, in some cases, the concentration of cutaneous lipids, in fluence the permeability of the skin to water. 6. Some amphibian speci es form a cocoon composed of various layers of stratum corneum; this c overs the body and reduces water loss considerably during the dry seas on. 7. It has been observed that the hydration capacity in some anuran s is related to the cutaneous vascularization in the ventral pelvic re gion, and that, in general, species of terrestrial habit have a greate r degree of vascularization than those of aquatic habit. 8. A number o f substances, including hormones such as vasotocin, oxytocin, thyroxin and prolactin, have some influence on the permeability of the skin to water. 9. The cutaneous mucus produced by the amphibians has great fu nctional diversity. In some anuran species it has a role in thermoregu lation and water economy. 10. The anuran genera Phyllomedusa and Litor ia wipe the skin with the legs so as to spread the lipid secretion fro m the cutaneous glands over the body surface. This secretion causes a marked reduction in the loss of body water. 11. The hydric balance in some anuran species is probably associated with the secretions of the granular glands, and in particular with the glycosaminoglycans found i n granular alveoli in the parotoid and paracnemid glands of bufonids.