Fig. 4. The effect of changing extracellular (A) and intracellular (B) pH on ammonia excretion rates of Sipunculus nudus isolated body wall musculature. Tissue samples were analysed after long-term exposure to normocapnic or hypercapnic media of different pH. ^*Ammonia excretion rate significantly different from the respective control value at pHe 7.9. Values are means ± S.D., N=5-6.