Experiments using 22Na-uptake and serial sampling techniques showed that during dehydration Na was taken up by the fat body in adult Periplaneta americana, but not in nymphs. Generally, accumulation of Na in the fat body was highest in animals which had little reserve lipid and in those which excreted the smallest amounts of Na during the dehydration period.

Dehydration caused little change in the Cl concentration in the haemolymph. From results of 36Cl-uptake experiments, it appears that the fat body is not involved in the regulation of haemolymph Cl during dehydration. In old adults, the hindgut was the tissue in which dehydration caused the greatest increase in 36Cl uptake.

The mechanisms which enable cockroaches to withstand dehydrating conditions are discussed.

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