Circulatory System

Periplaneta has an open type of circulatory system, in which the blood vessels are poorly developed and simply empty into a large body cavity called the haemocoel, so the colourless haemolymph (plasma plus phagocytic haemocytes) bathes the internal organs directly rather than staying confined to vessels. The heart is a single elongated, muscular tube lying mid-dorsally beneath the thorax, made up of 13 chambers, each with a pair of lateral openings called ostia through which blood enters from the surrounding sinuses; contraction of the heart then pumps this blood forward again into the sinuses through the anterior aorta. Thirteen pairs of triangular alary muscles, one pair per segment on either side of the heart, suspend the heart in position and, by their rhythmic movement, help draw haemolymph from the body cavity into the pericardial sinus surr …