Fish are characterized by a heart, consisting of an atrium and a ventricle, and a single circle of blood circulation. This is also typical for amphibian larvae. But as they grow and develop, with the onset of the process of metamorphosis, their organisms undergo significant changes, which also affect the circulatory system.
Adult amphibians have a heart with one ventricle and two atria (crocodiles have a four-chambered heart) and small and large circles of blood circulation. Despite the presence of two circles of blood circulation, they are not separated. This is due to the fact that amphibians are characterized by duality of respiration.
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