No results of investigation in natural history have been more amazing than those that show the marvelous richness of the sea in plant and animal life--not merely at its warm margin, but far out in the centre of what the ancients used to call "the desert of waters"; not only at its surface, but in its profoundest depths, and under the polar ice as well as amid the tropics. Sea populations differ somewhat according to situation, those of the shallow shore lines, which are of the "littoral" fauna, differ largely from those living in the open sea and belonging to the "pelagic" fauna, and there are surface swimmers, and others confined to the abysses; but virtually every class and subdivision in the animal kingdom is represented in greater or less variety in the zoölogy of the ocean. The list stretches from the merest monads to the huge sharks and still bigger whales. This multitude and diversity of animal life is possible in the sea because of an even greater plenitude of plants there, which furnish a never-failing food resource. Bacteria and blue-green algæ are at the base of this. Bacteria exist in all seas, as in all soils, and the fertility of nature above ground and under water depends on these microscopic organisms, whose numbers in the ocean are as incalculable as the grains of sand on its brink. In equal multitude are the diatoms, unicellular algæ with flinty cases, by which the waves are sometimes discolored over broad areas; and millions of other green plants, living alone, or in chains, minute in size, but each a chemical laboratory converting the salt water they absorb into meals for the animals that swallow them--animals in most cases almost as small and simple as the things they eat, and themselves destined to be sucked into the mouth of something a little bigger, to be in turn a tidbit for a third hungry mouth, and so on to the broiled mackerel for our own breakfast. THE PLANKTON AND ITS PHOSPHORESCENCE The assemblage of plants and animals that together float or swim at or near the surface of the ocean (or other water), say within a layer of water one hundred fathoms thick, is scientifically called _plankton_ of the sea. In the open ocean, the pelagic plankton is much alike all round the world of waters, although it varies a little in composition, and still more in relative abundance, being denser in temperate than in either tropical or polar latitudes; but nowhere is it absent. The "waste of waters" teems with life. The plankton of the shallow waters near continental shores, however, presents a decidedly different assemblage from the pelagic plankton.