Fig. 1. The temperature dependence of arterial pH and P_CO2 and of whole-body CO₂ stores (C_CO2) in tetrapods. Mean values of pH/T and of C_CO2/T (mmol kg^-1 body mass °C^-1) are as tabulated by Stinner et al. (1998). Mean values of logP_CO2/T, in °C^-1, are from the following sources (where there is more than one per species, the means and ranges of individual means are shown): filled circles, Coluber constrictor (Stinner et al., 1998), Varanus exanthematicus (Wood et al., 1981); open circles, Trachemys scripta (Jackson et al., 1974; Jackson and Kagan, 1976; Hitzig, 1982), Alligator mississippiensis (Davies, 1978), Chrysemys picta (Nicol et al., 1983; Glass et al., 1985), Chelydra serpentina (Howell et al., 1970), Dipsosaurus dorsalis (Bickler, 1981); filled triangles, Bufo marinus (Howell et al., 1970), Rana catesbeiana (Howell et al., 1970; Reeves, 1972; Mackenzie and Jackson, 1976). As described in the text, the crosses A and B show representative values for the two distinct groups of species (i.e. filled circles, and open circles together with filled triangles).