The open circulatory system is a type of circulatory system in which the cells bath in the blood directly. It is the characteristic feature of arthropods and mollusks. Grasshoppers are arthropods and have an open circulatory system. In the open circulatory system, the heart pumps the blood into the vessels with open ends.
Therefore, blood and interstitial fluid are not distinct and are collectively called hemolymph. The hemolymph comes out of the blood vessels and fills the large spaces called sinuses. The cells of their body bath in the hemolymph. The heart in arthropods has openings to allow the entry of the hemolymph into it.