Where the hemolymph meets the wall is where the rubber meets the road. Here we consider the walls and surfaces that hemolymph contacts. Walls are the portals to and from the moving liquid medium. Activities in or on the walls determine what enters and leaves the hemolymph and, hence, determines distribution to and from the body.

Walls include all surfaces contacting hemolymph: the external surfaces of organs such as the coverings of the alimentary tract, organs and muscles, the walls of the hemocoel itself, and the diaphragms. The diaphragms help direct the bulk flow of hemolymph. Central regions of the diaphragms direct flows fore and aft, but flows above and below a diaphragm may join along their lateral edges.

The circulating bulk volume of hemolymph transports molecules. Substances then diffuse from this bulk flow into surface layers of fluid along the walls before being absorbed. The local geometry and mobility of the surfaces and any microconfigurations abutting their interfaces help or hinder adsorbtion and desorbtion.

Volumes of hemolymph, pumping rates, and walking and flying determine how the hemolymph moves and circulates. Surface geometries and localized patterns of flow determine which molecules adhere to what points as well as the rates of reactions and release. Surface functions entail many highly irregular complex interactions that continuously evolve over the life of a bee or device.

To point up the similarities between bees and devices, consider now a hemocoel as if it were a microfluidic device.

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