Fig. 6. Two-dimensional distributions of oxygen partial pressure (P_O2) in the haemolymph of a 1.4 mm Hb-poor (top) and a 1.7 mm Hb-rich Daphnia magna (bottom), respectively, under different ambient oxygen partial pressures (P_O2amb). The P_O2amb values are indicated below each gallery. Note the different scaling of P_O2 in the pseudo-colour images as indicated by the colour bars at the top. During image acquisition, the optical focus was set to the median plane of the animal. For orientation, an image of the animal taken under transmission illumination is shown at the left side of each gallery.