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Fig. 5. The embryo stir-bar hypothesis. (A) In the absence of rotation, a large
oxygen concentration gradient will form due to the metabolic consumption of
oxygen by the embryo (depicted as stationary stir bar) and the unstirred
boundary layer of high oxygen concentration below the capsule surface. (B)
Embryonic rotation and ciliary activity (depicted as rotating stir bar)
function to mix the capsular fluid, causing a reduction in the size of the
oxygen gradient inside the capsule, a higher concentration of oxygen at the
embryo surface, and enhanced transfer of oxygen into the egg capsule. The
arrow size in A and B represents the relative size of the oxygen gradient
across the egg capsule membrane. Stir bar length is not representative of
embryo size (see Fig. 1).
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