bigger than those now existing. Their resemblance to Nautili and Ammonites is merely one of analogy. Mr. Drift-sand should also be closely examined for shells of the more minute Gasteropodous Mollusca. A wonderful variety of minute spiral univalve shells is found on our shores; though they are scarcely of so small a size as to come within the list of genuine microscopic objects. A simple pocket lens is sufficient to ascertain the characters of most. The different kinds of Rissoa, formerly included in the multifarious genus Turbo, are elegant little shells, whose spiral coils are variously sculptured or ribbed, sometimes in a very elaborate manner. Alder* has figured and described a considerable number of these small shells, many of them collected from driftsand. Others may be obtained by the gatherers of seaweeds with little trouble, if they will only preserve the sediment that collects in the water in which their seaweeds are washed. The Rissoce are vegetable-feeders, and live among the branches of the smaller sea-weeds, which are sometimes found as thickly covered with them as bushes are with snails. When the sea-weeds are plunged into fresh-water, the Rissoc are quickly killed and fall to the bottom, and may then be secured by simply straining the water through a piece of canvas. Many other minute and curious animals, and sometimes Diatomacea, may be collected in a similar way. Among the animated wonders of the sea, though not all of microscopic size, few tribes are more singular in structure and in their history, or more beautiful in their varied forms, than the Acalephæ, or Jelly-fishes, to whose "Annals Nat. Hist.," 1st Series. phosphorescence the luminosity of the sea is chiefly attributable. Many of these creatures are of strictly microscopic size, and so transparent that they can scarcely be seen in the water in which they swim, except when revealed by the motion of their cilia or the flashes of light which they send forth in the dark; others are of comparatively large size, and some are even three or four feet in length. The sea in all climates produces these simple creatures, and sometimes swarms with them in countless multitudes. Even on our own coasts I have seen the shore rendered offensive for miles in extent by the stranding of shoals of minute Medusa, each of which individually was scarcely bigger than a pea. But it is in tropical latitudes, and through the scarcely fathomable waters of the deep sea, that animals of this class display the greatest variety of form, and multiply in the greatest profusion. Here, too, the luminous species are of the largest size, and most brilliantly phosphorescent. Coleridge's description in the "Ancient Mariner" may convey some notion of their singular beauty:66 Beyond the shadow of the ship I watched the water snakes: They moved in tracks of shining white, "Within the shadow of the ship I watched their rich attire: Blue, glossy-green, and velvet black They coiled and swam; and every track Was a flash of golden fire." But it is difficult, in the most glowing description to convey an idea of the extraordinary effects produced by PHOSPHORESCENCE OF THE SEA. 219 the presence of such countless luminous points scattered through the waters of the ocean. Sometimes the whole surface, far as the eye can stretch, seems one sheet of phosphorescent sheen; while looking down into the water close to the ship large globes of fire are seen slowly moving along at various depths. The wake of the vessel, at the same time, displays the most vivid and varied scintillations, and the spray that breaks on her prow falls off like a shower of many-coloured sparks. One scarcely knows on which part of this wonderful display of fire-works to fix the attention. One after another attracts our gaze, and in its turn appears most beautiful. The phosphorescence is not constant; it is most vivid when the water is disturbed. Thus the passing of the vessel causes an illumination, long continued in the wake she leaves behind: while a sudden breeze sweeping over the surface will send a stream of light far across the sea, striking similar to the dartings of the aurora through the realms of air. Such are some of the glories that the tropical ocean presents to us; similar, but less brilliant illuminations are witnessed on our coasts, especially in warm evenings towards the close of summer, at which season vast multitudes of small Medusa frequently swim along the shore, entering into creeks and bays, and sometimes literally converting the shallower inlets into strata of living jelly. At ordinary times many beautiful kinds may be collected by dragging a small gauze net after the boat, just below the surface of the water. In calm weather these little creatures rise to the upper strata of water, and sink again when the sea is troubled. In structure, the Acalepha or Jelly-fishes are exceed 220 STRUCTURE OF MEDUSE. ingly simple, but not the less wonderful on that account. Our wonder is, indeed, the more excited when we find creatures of large size, as many of the Medusæ are, and endowed with considerable powers of perception, and some strength and agility, formed of a few delicate tissues filled with a fluid, to all appearance, not very different from sea-water. It is as if we had to investigate the structure of submarine bubbles. Take one of the largest of the race, weighing many pounds while living, and dry it. The whole contents of the body will either leak away or evaporate, and nothing will be left but some small shreds of membranous skin, forming a glistering stain on the surface of whatever object the Jellyfish was placed upon. The flesh is entirely composed of large cells of delicate structure, filled with a transparent fluid. But these cells are put together with the most rigid accuracy, and their arrangement is so varied that naturalists have had to distinguish numerous families and genera of Jelly-fishes. The number four prevails through the whole class. All the parts of the body are divisible by four, and mostly ranged in a radiate manner round a centre, so that either the animal is cruciform, or its internal parts are so arranged. But this form, though very general, is not universal :-some resemble long ribbons; others are oval or irregularly curved. The Jelly-fishes have been classed according to differences in their locomotive organs. Our most common species, referable to the Linnæan genus Medusa (but now comprising several distinct genera, according to the views of modern naturalists), are distinguished by an umbrella-shaped body, generally pellucid, from the THE PULMONIGRADE ORDER. 221 centre of which on the concave side depends a cluster of variously fringed and lobed vessels, which constitute the digestive system of the animal, while numerous slender fibres or tentacula hang from the border of the umbrellashaped disc. Such a creature resembles an animated mushroom, with its gills and stalk. Sometimes the stalk is reduced to a minute point, and there are very many modifications. The motion in all Jelly-fishes of this shape is accomplished by alternate contractions and expansions of the umbrella, repeated at regular intervals, something like the movement of the lungs in respiration, in allusion to which resemblance this order of Jelly-fishes has been called Pulmonigrade. The convex end of the umbrella is directed forwards, the fimbriated vessels and tentacula stream behind, and the creature is propelled with a steady and graceful motion, very rapid in some species. Unsightly and repulsive as the Jellyfish looks when stranded and lying exposed among sea-wrack on shore, it is a most beautiful animal when expanded in its native element and moving along in freedom. Nor is it so defenceless as its low organization and the softness of its parts may lead us to suppose. Many of the species are capable of inflicting a sharp and painful sting, sufficiently strong to paralyze the animals on which they prey, or perhaps to ward off danger when attacked by superior foes; while the long tentacles with which most of them are furnished are admirably adapted for seizing prey, as they adhere to whatever comes within their reach. A complete work on British Medusa is still a desideratum, but the task has been commenced by Professor Edw. Forbes, whose |