Pleopod beat of G. ingens was unaffected by pH at pH 7.1 and pH 7.9 but was lower at pH 8.7 due to increased cleaning activity. 2. The relationship between oxygen consumption rate, and pleopod beat was found to be semi-logarithmic. 3. The relationship between oxygen consumption rate and activity was unaffected by pH in the range of pH 7.1 and pH 8.7. 4. The per cent O extraction of oxygen by G. ingens was not statistically different at pH 7.9 and pH 8.7, but was greater at pH 7.1. 5. The ability of G. ingens to regulate its oxygen consumption was unaffected by pH in the range studied. 6. Since the increase in per cent O extraction at pH 7.1 does not improve the ability of G. ingens to regulate its oxygen uptake, it appears that there is a loss in effectiveness elsewhere in its respiratory system at this pH.
