 Amphibian skin is permeable to water . Gas exchange can take place through the skin ( cutaneous respiration ) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds . To compensate for their thin and delicate skin , amphibians have evolved mucous glands , principally on their heads , backs and tails . The secretions produced by these help keep the skin moist . In addition , most species of amphibian have granular glands that secrete distasteful or poisonous substances . Some amphibian toxins can be lethal to humans while others have little effect . The main poison @-@ producing glands , the paratoids , produce the neurotoxin bufotoxin and are located behind the ears of toads , along the backs of frogs , behind the eyes of salamanders and on the upper surface of caecilians . 
