In examining dead specimens we shall find that, contrary to what is usual, the male exceeds the female in size. I have a slide of a male, with the legs spread out before and behind, and the measurement from the claws of the first pair of legs to those of the fourth pair is 1¾ inches. The body is ¾ inch long. The whole surface is more thickly clothed with hair than is the case with other spiders, and the reason for this is obvious. This hairy body-covering serves to carry down into the water a layer of air, and the fringe of hair on the legs makes them efficient swimming organs. [Illustration: FIG. 58.--Cell of Diving Spider.] The Order of Mites will yield us subjects for our pocket lens. Mites are related to Spiders, but form a distinct Order. Like the Spiders, some are aquatic, though the most of them live on land. Many are parasitic, during the whole or part of their lives subsisting on the juices of their hosts: the food of others consists of organic _débris_, and these seem to be of benefit to man, since they act as scavengers. If we turn to page 96 we shall there find noted the points of difference in the arrangement of the main divisions of the body in Insects and in Spiders. In Mites the distinction between the cephalothorax and abdomen is lost, and the body is more or less oval or globular. In the perfect forms there are eight legs; but some, in their earlier stages, have only six. The mouth may be adapted for biting, though it is usually suctorial. In the Cheese Mites and some others breathing seems to be carried on through the skin, for there are no air-tubes; but in most Mites air-tubes, with two stigmata, are present. If we take a dip with the collecting-net in almost any pond we shall be pretty sure to capture some specimens of Water Mites of the genus Hydrach´na, easily recognizable by their bright coloration, their eight swimming legs thickly fringed with hair, and their unceasing activity. They may be kept in a bottle, or other small vessel, with some water-weed, and will forage for themselves. In Fig. 59 we shall see the points we have to look for in examining a Water Mite with a pocket lens. There should be no difficulty in making out in the specimen all the details shown in the cut. It may be that they will breed: if so we should avail ourselves of the opportunity of watching their development. Their life-history is somewhat curious, and is specially interesting from the fact that while Swammerdam had some faint perception of the true meaning of what he saw, De Geer, writing a hundred years later, drew entirely wrong conclusions from similar observations. It was left for Dugès to clear up the matter in the _Annales des Sciences Naturelles_, 1834. Before summarizing the account of the French naturalist it may be well to quote what Swammerdam and De Geer have said on the subject:--