Abstract
The uptake of fluid by the eversible ventral abdominal sacs of Petrobius brevistylis from a wet substrate is described. On lightly wetted filter paper the insects do not drink, and an insect with an initial fresh weight of 15mg can regain a 30% weight loss due to dehydration in 7 min when allowed access to filter paper wetted with distilled water. A similar insect would need 39 min to become replete when taking up fluid from a 0.33 osmole kg −1 NaCl solution. The length of time taken to become replete with distilled water was related to the size of the insect and the amount of water loss. Between 15 and 30% of the sodium ions present in each μl of an external NaCl solution entered with each mg of weight increase when the insects were allowed access to both a dilute and a stronger NaCl solution. Artificially everted sacs of anaesthetized insects absorbed fluid when in contact with NaCl or sucrose solutions that were hyperosmotic to the blood. The presence of an active transport mechanism for fluid in the eversible vesicles is discussed.
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