RECYCLING OF K-BASE EQUIVALENTS, AND FLUID BETWEEN GUT AND HEMOLYMPH IN LEPIDOPTERAN LARVAE(, ACID)

These studies show that the ileum and possibly the rectum of larval le pidopterans are important sites of recovery of base equivalents secret ed by the midgut. A model for recycling of fluid and solutes between g ut lumen and hemolymph is presented. In this model K+, bicarbonate, an d fluid return from posterior to anterior parts of the animal both in the form of hemolymph and as Malpighian tubule fluid flowing in tubula r loops closely apposed to the hemolymphal surface of the midgut. This arrangement appears adapted to maximize the efficiency of excretion o f uric acid and other weak acids, while recycling K+ and bicarbonate.