Amphibians lead aquatic and terrestrial lifestyles. In this regard, they have formed such structural features and physiology as:
1) mucus-coated skin in which atmospheric oxygen dissolves when breathing;
2) lever limbs for movement on land;
3) the skeleton is clearly differentiated into departments;
4) lungs for atmospheric breathing;
5) two circles of blood circulation and a three-chambered heart, providing a partial separation of blood into venous and arterial;
6) there is a middle ear, closed outside the eardrum.
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