The object of this paper is to discuss the recently discovered encystment of Tardigrada, as far as our imperfect knowledge permits; to compare the process with that observed in certain low groups of the Acarina, in which the Tardigrada are generally considered to have their nearest relatives; then to inquire whether these new facts throw any light on certain puzzling facts in the physiology of the Tardigrada and Acarina, such as the retrogression which produces the simplex forms of Tardigrada, and which is said to accompany each moult of the Acarina; and lastly, if they contribute anything towards settling definitely the systematic position of the Tardigrada.

In this paper the results of observations of the elevation of the boiling point of aqueous solutions of electrolytes are given, and a few results of observations of the depression of the freezing point, together with conductivity data obtained by observations of conductivity at about 99·4° and 0° Centigrade.