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Malpighian tubulesthe excretory organs of some ARTHROPODS, such as insects and arachnids, that collect wastes from the body fluids and discharge them into the hind gut. They are tubular glands which open into the anterior part of the hind gut, the other end being closed and bathed in the animal's blood in the HAEMOCOEL.
The slender tubules ar orm potassium hydrogen carbonate and uric acid. The KHCO3 and some water are reabsorbed from the tubules into the blood; further water is absorbed by the rectal gland and crystals of uric acid are voided into the gut for excretion.