Fig. 1. Mass-specific O₂ consumption rates in Pseudis paradoxus tadpoles and froglets measured at 25°C on exposure to water of variable O₂ tension (mean of initial P_O2 values) with free access to air. Each point represents the mean ± 1 s.e.m. of N>7 animals staged according to Cais after Gosner (Cais, 1982; Gosner, 1960) and measured individually. The data are pooled into groups of stages representing distinct developmental steps during the larval period. There is no significant effect of O₂ tension on the rates; most variability is attributable to developmental stage (F=48.2, P<0.0001).