Maddrell, S. H. P. 1971. The mechanisms of insect excretory systems. Adv. Ins. Phvsiol. 8: 200-331.

Water Relations

Terrestrial arthropods are subject to water loss (Barton-Browne 1964, Stobbart and Shaw 1974) from excretion, in the feces, and through the cuticle, including that lining the respiratory system. The loss is especially intense in species living in arid environments. Water is gained primarily in the food but also by drinking and general absorption from humid air. Special organs of conservation are also present in association with the hindgut, whose normal functions include reabsorption of water from the feces. One of these, the cryptonephrid-ium, incorporates the distal ends of Malpighian tubules which loop back onto or into a thickened portion of the rectum. Water is recycled from the latter back into the tubules and reused; feces from these insects emerge in a very dry state.

Aquatic insects have salt and water control problems different from but no less severe than those faced by terrestrial types. Since the hemolymph is hypertonic to the outside medium, there is a constant tendency for water to pass into the insect through the cuticle. This uptake is counterbalanced by a copious liquid outpouring, which, however, results in a loss of salts. This is corrected by reabsorption by the rectum.

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