And the greater part, if not the whole, as we now know, is due to uncountable multitudes of jelly-creatures, floating close to the surface, each contributing its tiny share to the radiant sheen. Sometimes they are large enough to be visible to the naked eye, but more generally they are minute microscopic beings, far too small individually to be seen by us, yet apparent in the mass by their united brilliance. If millions of their glowing lamps shine in ocean’s deeper parts, we need no longer marvel to find deep-sea animals with large and well-developed eyes. While on this subject, it should be added that the Medusæ have not a monopoly of ocean-lamps. Other creatures share in the task of lighting up those midnight depths. Not long since two new species of fishes were discovered off the Azores, both of which possessed delicate organs of light-giving power. In one of them the rows of tiny lamps could be used or hidden “at will”--allowed to shine upon the world around, or shut off by a thick dark skin, somewhat after the fashion of a policeman’s “dark lantern.” Cuttlefishes too have been found carrying natural lamps for sub-ocean use. CHAPTER XX. ARMOURED MYRIADS AND MONSTERS “The Sea hath its Pearls.”--LONGFELLOW. “From out thy slime The Monsters of the Deep are made.”--BYRON. Among the multitudinous hosts of living creatures which throng the Ocean, vast hordes are furnished with some kind of protective armour, the better to take their part in the ceaseless warfare for existence. Though the armour differs widely in different kinds of animals, they offer one and all a great contrast to the soft jelly-like Medusæ. Starfishes and Sea-urchins, for example, are guarded by tough or hard skins, with actual plated armour and sharp prickles. Limpets are sheltered behind single firm shields, and in any moment of peril become instantly glued by suction to a rock. Oysters dwell within stout bivalve shells. Hermit-crabs carry with them empty purloined shells, of other creatures’ construction. Crabs and Lobsters wear strong suits of sheltering armour, joined together bit by bit, as knights and squires of old were clothed from head to foot in the many “pieces” of a mediæval soldier’s military suit. The armoured hosts belong to various divisions in the Animal Kingdom,--starfishes and sea-urchins to one; limpets and oysters to another; crabs and lobsters to a third. And all three, together with microscopic jelly-specks and sponges and coral-polyps and medusæ, belong to a much greater Division, which embraces all “Invertebrate” or Backboneless creatures. If they have not backbones and ribs, they have skeletons of a kind. Only, as a general rule, the skeletons lie outside or are visible through the transparent body, instead of being hidden away inside, as in most fishes. The prickly-skinned starfishes and sea-urchins are familiar objects with most of us.