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Fig. 2. Effect of external gills on oxygen levels that (A) limited metabolic rate
in red-eyed treefrog embryos and tadpoles and (B) induced hatching, measured
using closed-system respirometry. External gills improved oxygen uptake for
embryos in terrestrial eggs, lowering both Pcrit and the
PO2 that induced hatching. Embryos without
gills were oxygen limited even in air (
20.5 kPa). External gills had no
effect on the Pcrit of hatched tadpoles in water. Data are
means ± s.e.m.; N=11 animals per treatment.