Rectal Absorption in the Desert Locust,Schistocerca GregariaForskål: III. The Nature of the Excretory Process*

Abstract

1. The physiology of the excretory system and its role in salt and water balance have been studied in the desert locust, Schistocerca gregaria. 2. Collections and analyses were made of hindgut fluid (derived from the Malpighian tubules) and rectal fluid from locusts kept under various dietary régimes. 3. In starved locusts supplied with tap water very little fluid accumulates in the rectum, the output of the Malpighian tubules being almost completely reabsorbed. Relatively more salt than water is reabsorbed with the result that the rectal fluid attains a lower ionic concentration but higher osmotic pressure than the haemolymph. No fluid is voided. 4. In starved locusts supplied with hypertonic saline the rectum is distended with, fluid which has an osmotic pressure and ionic concentration considerably above that of the haemolymph. Very little fluid is voided. 5. Substantial elimination of fluid from the rectum occurs only in fed locusts, in association with the voiding of faeces. 6. These results are discussed in relation to the mechanism of osmotic and ionic regulation.