-INTERNAL FEATURES-

The central nervous system consists of brain and ventral nerve cord. The brain is composed of two large ganglia that surround the esophagus. The supraesophageal ganglion is bilobed: the protocerebrum processes optic information and is the origin of complex behaviors; the tritocerebrum mainly controls the normal body functions. The subesophagal ganglion innervates the chelicerae. Locomotion is controlled by both ganglia. A pair of circumesophageal connectives links the two ganglia. The nerve cord, which runs posteriorly along the length of the animal, consists of seven ganglia connected by pairs of fibres.

Scorpions' tactile and chemical sense

Scorpions interpret vibrations by hairs (trichobothria) that are deflected best by air vibrations originating perpendicular to one plane. These hairs are situated on the pedipals along different planes, thus allowing scorpions to detect the direction of air movement (e.g., to detect predators and catch aerial prey). Chemoreceptors are located in the oral cavity (for taste) and the pectines. Receptors in the pectines are used by some species to locate some prey. Males use their pectines to detect pheromones produced by receptive females.

Digestion and excretion

Digestion begins outside the mouth. The preoral cavity is supplied with digestive juices from the gut that semi-digest the food before it enters the mouth. Setae in the preoral cavity filter undigestible material such as prey exoskeleton. These particles are matted together and expelled. Food passes from the mouth to the pharynx to the esophagus to the midgut to the hindgut and is expelled through the anus. The muscular pharynx acts as a pumping organ drawing food into the body. Excretion wastes are expelled through the anus with feces.

Circulatory system

The dorsal tubular heart runs the length of the mesosoma. A pacemaker contracts the heart rhythmically. Hemolymph (blood) flows via the anterior aorta to the prosoma and from the posterior aorta to the metasoma. The anterior aorta branches into the cephalic and cerebral arteries and to smaller arteries that carry blood to each limb and to the nerve cord. Arteries branch further and eventually empty into blood sinuses. Blood sinuses are extensive and bathe most tissues. Most gas and material exchange occurs there. Blood returns via sinuses and veins into a pericardial sac surrounding the heart, entering it through seven pairs of slitlike ostia. Blood is a colourless fluid containing proteins abd salts. There aren't blood cells.

Book lungs

They consist of a cavity and internal parallel leaves(lamellae) of thin cuticles across which gas exchange occurs. A sinus surrouunds the book lungs, and blood is pumped in and out indirectly by the heart; the cardiac pulse is transmitted by ligaments attached to the sinus. Ventilation occurs when individuals move.