Figure 7. The countercurrent heat-exchanger in the head of kissing bugs.

(A) Sagittal section of the head of Rhodnius prolixus (scale bar, 100 µm). (B, C) 3-Dimensional reconstruction of the head based on frontal and sagittal sections. A: Detail of the countercurrent heat exchanger at level of the brain. (B) General view of the head and circulation routes of ingested blood (red) and haemolymph (blue). Note the close association between the aorta (ao) and the alimentary canal (oe) at the level of the brain (b). In beige, the muscles of the cibarial pump (cp). Directions of flowing fluids are indicated by arrows: red/black arrows indicate the direction of the ingested blood circulating in the alimentary canal; blue/black arrows indicate the flow direction of the haemolymph. Red arrows on top indicate the heat loss to the environment by both convection and radiation. Vertical blue/red arrows indicate the countercurrent heat transfer between aorta and oesophagus fluids and the consequently refreshed blood that continues toward the thorax (purple arrow). The exact location of the system is behind the compound eyes, as can be appreciated in Figures 2–4.