Aspects of ionic regulation in certain terrestrial pulmonata

1. On crawling over a wet surface, dehydrated specimens of Otala lactea and Helix aperta absorb water into the blood until, within 2–3 hr, the concentrations of sodium, potassium, calcium, magnesium and total solutes have fallen to approximately constant levels which are similar in the two species. 2. Though the two species are ecologically dissimilar, the cocentrations in the blood of sodium, potassium and total solutes vary in much the same way. Sodium varies between about 60 and 180 mM/kg of water, although in inactive specimens the concentration usually exceeds 90 mM/kg of water. The concentration of potassium is generally 2·7-7·0 mM/kg of water and is correlated with that of sodium, feeding apparently having no effect on the relative proportions of the two ions. 3. Whilst the composition of the blood in the Pulmonata is very variable, in seven of the nine species for which data are available the empirical expression (0·065 Na + √ Mg)/(K + √ Ca + 8), where concentrations are expressed as mM/l or mM/kg, has a value of 0·49-0·52