Fig. 4. Davenport diagram depicting passive buffering of intracellular pH (black lines) in two cephalopod species. Similar increases in CO₂ partial pressure (in mmHg; 1 mmHg=133.3 Pa; represented by the blue isopleths and numbers) will result in dramatically different changes in intracellular pH in shallow-(Stenoteuthis oualaniensis) and deep-living (Japetella heathi) cephalopods. Buffering data are from Seibel et al. (1997).