Hemolymph

Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues.

It is the major tissue type of the open circulatory system characteristic of arthropods (for example, arachnids, crustaceans and insects).

Oxygen-transport systems were long thought unnecessary in insects, but ancestral and functional hemocyanin has been found in the hemolymph.

[4] In the grasshopper, the closed portion of the system consists of tubular hearts and an aorta running along the dorsal side of the insect.

Coordinated movements of the body muscles gradually bring the hemolymph back to the dorsal sinus surrounding the hearts.

The hemolymph of lower arthropods, including most insects, is not used for oxygen transport because these animals respirate through other means, such as tracheas, but it does contain nutrients such as proteins and sugars.

[5] Note that the term "ostia" is not specific to insect circulation; it literally means "doors" or "openings", and must be understood in context.

Such nucleating agents have been found in the hemolymph of insects of several orders, i.e., Coleoptera (beetles), Diptera (flies), and Hymenoptera.

[6] Hemolymph is composed of water, inorganic salts (mostly sodium, chlorine, potassium, magnesium, and calcium), and organic compounds (mostly carbohydrates, proteins, and lipids).

These include inositol, sugar alcohol, hexosamines, mannitol, glycerol and those components that are precursors to chitin.

Only in a few insects living in low-oxygen environments are there hemoglobin-like molecules that bind oxygen and transport it to the tissues.

Collection of hemolymph from a worker honeybee.
A grasshopper has an open circulatory system , where hemolymph moves through interconnected sinuses or hemocoels, spaces surrounding the organs.
Above is a diagram of an open circulatory system. An open circulatory system is made up of a heart, vessels, and hemolymph. This diagram shows how the hemolymph is circulated throughout the body of a grasshopper. The hemolymph is first pumped through the heart, into the aorta, dispersed into the head and throughout the hemocoel, then back through the ostia that are located in the heart, where the process is repeated.