4. DEEP-SEA FISHES. Two of them--_Melanocetus murrayi_ and _Melanocetus indicus_--are related to the Angler of British coasts, but adapted to life in the great abysses. They are very dark in colour, and delicately built; they possess well-developed luminous organs. The third form is called Chauliodus, a predatory animal with large gape and formidable teeth.] [Illustration: FLINTY SKELETON OF VENUS FLOWER BASKET (EUPLECTELLA), A JAPANESE DEEP-SEA SPONGE] [Illustration: EGG DEPOSITORY OF _Semotilus Atromaculatus_ In the building of this egg depository, the male fish takes stones from the bottom of the stream, gripping them in his mouth, and heaps them up into the dam. In the egg depository he arranges the stones so that when the eggs are deposited in the interstices they are thoroughly protected, and cannot be washed down-stream. 1, dam of stones; 2, egg depository; 3, hillock of sand. The arrow shows the direction of the stream. Upper fish, male; lower, female.] The "floating sea-meadows," as Sir John Murray called them, are always receiving contributions from inshore waters, where the conditions are favourable for the prolific multiplication of unicellular Algae, and there is also a certain amount of non-living sea-dust always being swept out from the seaweed and sea-grass area. Swimmers and Drifters The animals of the open sea are conveniently divided into the active swimmers (Nekton) and the more passive drifters (Plankton). The swimmers include whales great and small, such birds as the storm petrel, the fish-eating turtles and sea-snakes, such fishes as mackerel and herring, the winged snails or sea-butterflies on which whalebone whales largely feed, some of the active cuttles or squids, various open-sea prawns and their relatives, some worms like the transparent arrow-worm, and such active Protozoa as Noctiluca, whose luminescence makes the waves sparkle in the short summer darkness. Very striking as an instance of the insurgence of life are the sea-skimmers (Halobatidae), wingless insects related to the water-measurers in the ditch. They are found hundreds of miles from land, skimming on the surface of the open sea, and diving in stormy weather. They feed on floating dead animals. The drifters or easygoing swimmers--for there is no hard and fast line--are represented, for instance, by the flinty-shelled Radiolarians and certain of the chalk-forming animals (Globigerinid Foraminifera); by jellyfishes, swimming-bells, and Portuguese men-of-war; by the comb-bearers or Ctenophores; by legions of minute Crustaceans; by strange animals called Salps, related to the sedentary sea-squirts; and by some sluggish fishes like globe-fishes, which often float idly on the surface.