Fig. 2. Tritonia diomedea; respiration measurements of early embryos at two temperatures. Each datum point shows the oxygen consumed in one single respiration chamber, plotted against the number of capsules in the chamber. Respiration of an individual capsule was estimated from the slope of the regression line at each temperature (orange circles, 21°C; b=863.1, r²=0.99; blue circles, 12°C; b=495.1, r²=0.95). Error was calculated as the s.e.m. of the slope (s.e.m. 21°C=201.6; s.e.m. 12°C=52.6). The non-zero intercepts are an unexplained but very common phenomenon in microrespiration measurements, and do not affect estimates of respiration rate derived from the slope; see discussion elsewhere (Marsh and Manahan, 1999).