Circulation Time

Hemolymph does not always circulate in our usual pattern. Witness the mosquito feeding on your hand. Observe the pumping abdomen filling with blood and the heart rapidly contracting forcing blood forward as moving abdominal viscera and a distending blood-filled midgut stir the hemocoel. Under a microscope you can see ripples in the ventral diaphragm progressing backwards.

In embryonic and pupal stages, even after hearts develop, hemolymph may not circulate rhythmically, but hemolymph circulates before the dorsal vessel forms. Once the dorsal vessel begins to pump, however, flow follows the generalized dorsal, lateral and ventral pathways previously established around organs and skeletal elements. Attachments of the massive muscles for walking and flight complicate the patterns of flow through the thorax. The usual pattern, providing impetus for flow, is that the accessory pumping organs, contractions of the alimentary canal, respiratory movements, and contracting muscles and other organs assist the heart.

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