that we may briefly define the species Artemia ( Callaonella ) Jelskii , for instance, as the Artemia of density 1000ã1010 (NaCl), or the typical A. salina , or principalis , as the Artemia of density 1018ã1025, and so forth. It is a most interesting fact that these Artemiae, under the protection of their semi-permeable skins, are capable of living in waters not only of great density, but of very varied chemical composition. The natron-lakes, for instance, contain large quantities of magnesium
sulphate; and the Artemiae continue to live equally well in artificial solutions where this salt, or where calcium chloride, has largely taken the place of sodium chloride in the more common habitat. Furthermore, such waters as those of the natron-lakes are subject to very great changes of chemical composition as concentration proceeds, owing to the different solubilities of the constituent salts. It appears that the forms which the Artemiae assume, and the changes which they undergo, are identical or {130} inôÙdisôÙtinôÙguishôÙable, whichever of the above salts