While swimming about in the water the spider has a most striking appearance, its abdomen almost resembling a globe of quicksilver. This is because the body is enveloped in a bubble of air, retained largely by the long hairs with which it is clothed. Thus it carries its atmosphere about with it, and as often as not it swims with its back downwards, which has the effect of bringing the bulk of the air-bubble towards its ventral surface, where the breathing pores are situated. Now when the dome-shaped web is ready to be filled with air the spider rises to the surface, lifts its abdomen above it, and brings it down with a flop, thus imprisoning an extra large air-bubble which it embraces with its hind-legs by way of holding it more securely, and then, swimming rapidly down by means of its other legs to the web it discharges its load of air beneath the downwardly directed mouth of the dome. By a frequent repetition of this process the dome is at length filled and converted into a veritable diving-bell, in which the spider can exist quite comfortably until the supply of oxygen in the imprisoned air is exhausted and has to be renewed. From this base it issues forth to feed upon fresh-water insects and crustaceans, sometimes even attacking small fishes. The proceedings of the male _Argyroneta_ in the mating season are very curious. He seeks out the tent of a female and sets up his own establishment—generally somewhat smaller—close at hand, filling it with air in the approved manner. He then builds a sort of corridor uniting the two domes, and when this is complete he bites through the female dome, thus uniting the two air reservoirs by means of a connecting tube. Not seldom it happens that the female is in no mood for dalliance, and a battle royal ensues, with disastrous results to both domiciles and the tube that connects them. The male, however, is in this case well able to hold his own, for he is larger than the female, a phenomenon elsewhere unknown in the spider realm. _Argyroneta_ lives for some years, and makes two diving-bells each year—one near the surface in summer and one at a greater depth in winter. It was thought at first that one was constructed especially for receiving the eggs and the other as a habitation, but the egg-cocoon may be found in either, for there are two broods in the course of the year. The winter dome is of very dense silk, glossy in appearance, and giving the effect of a uniform sheet of silky material rather than a fabric. Moreover its mouth is closed, and the spider remains inactive within. It is this winter domicile that is most frequently found in the shells of molluscs. The egg-cocoon is also dome-shaped, having a convex upper and a flat under surface. The newly hatched young inhabit their mother’s tent for a time and then set forth in the water to seek their living and set up establishments on their own account.