Blood Circulation in Other Animals

The problem of transferring substances from one part of the body to another faces all organisms. In protozoa, circulation occurs through diffusion and movement of the cytoplasm. In coelenterates and flatworms, the body cavity is used to transport substances. Annelids have a primitive circulatory system consisting of vessels and “hearts.”

Arthropods and mollusks have a heart, blood vessels and blood cells. In vertebrates, the circulatory system is the most developed. During the process of evolution, the structure of the heart changed - chambers appeared that separated aerated and non-aerated blood. This made it possible to maintain a high level of metabolism and body temperature in birds and mammals.