Fig. 8. Responses in internal oxygen partial pressure (P_O2) and heart rate (fH, open squares) of differently sized (small, medium, large: 1.5±0.12, 2.5±0.3, 3.3±0.13 mm) Hb-poor and Hb-rich Daphnia magna to decreasing ambient oxygen partial pressures (P_O2amb). The haemolymph P_O2 is given for the carapace lacuna (loading P_O2, open circles), the dorsal lacuna (open diamonds), the heart region (open triangles), and the central body region (unloading P_O2, closed triangles). The dotted lines represent lines of identity where P_O2=P_O2amb.