Insect circulatory system

Insects are a sealed unit in the sense that they have an open system. There is no blood vessel system like vertebrate animals. The interior of the main body is a hemocoel where the "blood" (hemolymph) percolates over and around the tissues which consist of one, or a only few, cell layers rather than thick organs like vertebrates. The aorta pumps the hemolymph forward from the posterior and ensures mixing. Auxiliary pumps ensure hemolymph cycling to the legs, wings and antennae.