Allied to the bristle-tails, and usually grouped with them in the same order, are the little Spring-tails, some species of which may often be seen huddled together on the surface of the water of a rock pool. They are so small that, unless closely examined, they may be mistaken for particles of floating inorganic matter which have been blown into a sheltered corner of the pool, and this idea may be strengthened by the fact that these minute creatures _are_ driven by the wind into such sheltered spots. But when we disturb them their true nature immediately becomes apparent, for they may then be seen to move about on the surface of the water, sometimes creeping on the surface film, and clambering on the adjacent rock or weed, or leaping more or less vigorously, in which latter case their bodies do not become wetted, the surface film remaining unbroken by their exertions. And even when the rising tide drives the spring-tails into crevices where they remain submerged, perhaps for hours together, their bodies still remain dry, the water being kept off by numerous short bristles and prominences with which they are furnished. When we examine a spring-tail by means of a lens we observe that it has no traces of wings, but that each of the three segments representing the thorax bears a pair of short legs, and that the abdomen consists of only five or six segments. The head is furnished with a pair of jaws, and the antennæ, which are short and thick, are composed of but few joints--never more than six in number. Some spring-tails live among the refuse washed up on the beach, where they may be seen jumping about in company with the sandhoppers when the material is disturbed. Such is the case with _Isotoma maritima_, the illustration of which shows the forked tail that enables the little animal to jump about so vigorously. But some of the marine spring-tails are not so true to their name, since they are not provided with this characteristic jumping organ, and have to content themselves by creeping about slowly with the aid of their short legs. One of these springless spring-tails (_Anurida maritima_) is one of the commonest of the group, and is distributed over almost every part of our coast. Passing over several orders of insects which do not seem to have any marine representatives, we come to the _Diptera_ or two-winged insects, of which the familiar house-fly is a type, and here we have to deal with those troublesome creatures that literally swarm in the neighbourhood of the matter washed up to the highest level of the tide during the whole of the summer months. But although these insects are so very numerous, we do not find among them a particularly large number of species, their abundance being due more to the extreme prolificacy of those that occur.