Reviewing the Path

During normal circulation in the worker bee, the heart pumps hemolymph forward into the aorta during systole. The blood then enters the perivisceral sinus in the head as the aorta opens out over the brain. At this time, blood also exits the dorsal vessel through the excurrent ostia. Valves within the incurrent ostia close during systole, so that hemolymph does not leave the dorsal vessel as the heart squeezes. Were the incurrent ostia in the heart to open during systole, pressure would be lost, and less hemolymph would pass through the aorta.

As hemolymph leaves the aorta to enter the perivisceral sinus, the new hemolymph entering the sinus forces the hemolymph from the last systole backwards through the sinus. Movements of the dorsal diaphragm aid this flow. Slowly moving hemolymph washes over the organs and tissues where exchange occurs. As the heart pump fills during diastole, hemolymph leaves the periv-isceral sinus in the abdomen to enter the heart. As the heart sucks hemolymph into itself during filling, loss of hemolymph from the hemocoel promotes rearward flow of blood through the perivisceral sinus. Presumably, a moving perineural or ventral diaphragm encourages blood to flow around the ventral nerve cord supplying it.

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