ABSTRACT
The myxinoids are a marine group of cyclostomes whose blood shows some similarities to the sea water in Which they live, even when they are moved to more dilute environments. Reviews by Morris (1960) and more recently by Robertson (1963) emphasize that the plasma is slightly hypertonic to the environment and that during the course of ionic regulation divalent ions are reduced in the plasma relative to sea water (Smith in Cole, 1940; Robertson, 1954; Bellamy & Chester Jones, 1961). Thus the main work of ionic regulation seems to fall on the tissues themselves. Here, potassium partly replaces sodium, whilst phosphate and perhaps amino acids take the place of chlorides (Robertson, i960; Bellamy & Chester Jones, 1961). The osmotic deficit between the plasma and the tissues seems to be made up in part by unidentified organic acids and by large amounts of trimethylamine oxide which, according to Bellamy & Chester Jones, reaches concentrations comparable with those found in marine elasmobranchs.
