Printed in Great Britain ACTIVE TRANSPORT OF MAGNESIUM BY THE MALPIGHIAN TUBULES OF THE LARVAE OF THE

1. Larvae of Aedes campestris can survive in water containing up to 100 Mg even though they ingest and absorb into the haemolymph consider-able amounts of magnesium-rich fluid. 2. Isolated Malpighian tubules, unlike those of Rhodnius and Carausius secreted fluid containing elevated concentrations of magnesium. This transport displayed saturation kinetics, the half-maximal rate being at approxi-mately 2-5 mM Mg. 3. Active transport of magnesium was demonstrated by the secretion of this cation against a tenfold concentration gradient and an electrical poten-tial difference of 15 mV. 4. Magnesium ions are not required for fluid transport, which proceeds independently of magnesium transport. As a result fluid which is secreted slowly contains higher concentrations of magnesium than that which is secreted more rapidly. 5. Magnesium is transported by isolated Malpighian tubules fast enough to account for the observed excretion of magnesium in living mosquito larvae