The marine relatives of our Striders have some curious habits. Some of them live out at sea, hundreds of miles from land, where they are thought to feed upon the dead bodies of small animals. When the surface of the sea is calm they glide in colonies quickly over the surface, showing great skill in diving, but if the sea begins to become agitated they immediately disappear from the surface. Perhaps the most remarkable habit which a surface insect has is that possessed by some of the allies of the Skaters, which not only swim in the water, but actually run on the _under_ side of the surface film. It would be very interesting to know how such a habit was acquired. Another interesting group of insects are those which breathe air, as the surface film insects, yet seek their food below the surface. These insects are compelled, on account of their air-breathing habits, to repeatedly visit the surface or communicate in some way with a fresh supply of air. [Illustration: INSECTS. Life-size. FROM COL. CHI. ACAD. SCIENCES. COPYRIGHT 1900, BY A. W. MUMFORD, CHICAGO. Archimerus calcarator Oncopeltus fasciatus Ranatra fusca Galgulus oculatus Nezara hilaris Leptoglossus phyllopus Benacus griseus Zelus bilobus Metapodeus femoratus Conorhinus sanguisugus Cicada septemdecim Platycotis sagittata.] We have two families of the large-sized water beetles, common in our ponds and streams. The Predaceous water-beetles and the Water-scavenger beetles. These are easily recognized, because in the former, the antennæ are thread-like and not enlarged at the tip. While the members of the Water-scavenger family have the antennæ enlarged or club-shaped at the tip. The Predaceous water-beetles are often quite common under electric lights, where they have been attracted by the intense light. Their large size and clumsy movements, when out of water, attract attention. But when seen in water their skill as swimmers is in striking contrast to their awkward movements made on land. The hind legs are flattened and very powerful, the surface being increased by a fringe of strong hairs on the inner side. In swimming the stroke is made by both legs at once. Perhaps the most interesting facts about these beetles are those associated with their method of breathing.