The Vapour Pressures of the Blood of Arthropods from Swift and Still Fresh Waters

Abstract

It has been shown that the oxygen consumption of caddis larvae and mayfly nymphs from swift streams is considerably greater than that of comparable species from still waters, and that within one species of isopod Crustacea, Asellus aquaticus, individuals from swift water consume more oxygen than those from slow water (Fox and Simmonds, 1933; Fox, Simmonds and Washbourn, 1935).It has also been shown that the oxygen consumption of fresh-water Crustacea is greater than that of their marine relatives (Fox and Simmonds, 1933). Now, in marine invertebrates, the osmotic pressure of the blood is close to that of sea water, whereas in fresh-water invertebrates the difference between the osmotic pressures of blood and water is great. In fresh water compared with marine Crustacea, then, a higher oxygen consumption goes together with a considerable inequality between internal and external osmotic pressures.