The open circulatory system of the 'grasshopper' is made up of a heart, vessels, and hemolymph; where hemolymph moves through interconnected sinuses or hemocoels, spaces surrounding the organs. The hemolymph is pumped through the heart into the aorta (main artery), dispersed into the head and throughout the hemocoel, then back through the ostia (pores) in the heart and the process is repeated.

In anthropods (an invertebrate), the open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes, where the organs are directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid, that is called hemolymph or haemolymph. Hence, hemolymph is analogous to the blood in human or other vertebrates.

Hemolymph fills all of the interior hemocoel of the body which is composed of water, inorganic salts (sodium, chloride, potassium, magnesium, and calcium) and organic compounds (carbohydrates, proteins, and lipids).

The primary oxygen transporter molecule is hemocyanin (proteins). The hemocyanins are proteins that unlike the hemoglocin in red blood cells are not bound to blood cells but are instead suspended directly in the hemolymph.

More Info: en.wikipedia.org