An arrangement of the excretory system in certain beetles and lepidopteran larvae in which the distal blind endings of the Malpighian tubules are held against the wall of the rectum by a perinephric membrane. A high concentration of ions is established in the tubules, which draws water from the gut by osmosis. This creates a highly efficient mechanism for water conservation in species, such as mealworms (e.g. Tenebrio spp.), that feed on very dry materials.
Subjects: Biological Sciences.