Fig. 7. Oxygen partial pressure (P_O2) distribution in the haemolymph in the median plane of Daphnia magna. Left: 1.7 mm Hb-rich animal at an ambient oxygen partial pressure (P_O2amb) of 1.7 kPa. Right: 1.4 mm Hb-poor animal at a P_O2amb of 5.1 kPa. Note the marked differences in the steepness of the P_O2 gradients between both animals. The orientation of the animal with respect to the viewer is indicated by the positional information and by the small sketch in front left.