MARINE INSECTS. Insects have not only invaded rivers and lakes, they have estab lished themselves to some extent at least, along the margin of the sea. On a sunny day by the shore myriads of flies may be seen hovering over the seaweed cast up by the tide. These have been developed from grubs which live and feed in the decaying weed, and are able to bear immersion twice daily. Around the rock-pools many midges may be noticed. Their grubs feed on growing green seaweed, and spend their whole life in the salt water, breathing the dis solved air, as do their fresh-water relations, by means of gill-filaments, or simply through the -surface of the skin. Many species of beetles inhabit the shore, and are submerged twice daily, when they lurk under stones or burrow into the sand; their hairy bodies are not easily wetted, and in one of the best-known marine beetles (Alpus) there are paired air-sacs in the hind-body which are believed to act as reser voirs for breathing while the tide is up. Sev eral kinds of very small may be seen on the surface of the rock-pools at low-tide; probably when the water rises they retire into crevices of the rocks. They are covered with a very fine, dense pile, and it seems impossible to wet them.
The absence of wings is a common character among the sea-shore insects. The beetles of the genus Aepus are wingless, and so is the small bug "Wapiti/us often found in their company, as well as the female of the midge Clunio, whose mate, though winged, appears not to fly, but to use his wings as sails as he skims over the surface of the rock-pools. °The tendency
of insects on oceanic isles to lose their wings has often been noticed') says Carpenter, °and the loss of the power of flight explained as an ad vantage, since insects which do not fly cannot be blown out to sea. Possibly the absence of wings in so many sea-shore insects can be ex plained in like manner. Several genera of pond-skaters have one or two species which frequent the water of estuaries and harbors; these are in all cases wingless, though their fresh-water relations are, as a rule, winged." The extreme of adaptation to marine life is shown by the bugs of the genus Halobates, also belonging to the family Hydrometrichr, with their short anchor-like fore-legs and their im mensely long and slender middle and hind-legs, the middle shin and foot being fringed with long hairs. The elongate wingless fore-body of these insects and the greatly reduced hind-body give them a most peculiar and characteristic appearance, and the dense pile wherewith they are clothed keeps them dry. They have been observed gliding over the calm seas of the tropics, often hundreds of miles from land, or clinging to drifting substances whence they could suck food. Consult Carpenter, G. H., 'Insects, their Structure and Life' (1899) ; Miall, 'Natural History of Aquatic Insects' (1895).