Vickipedia

SPONGE (Spongia), a genus which originally included all the numerous genera and species of the family Spongiadæe, all of which are still commonly spoken of by naturalists as sponges, although in its more popular sense that term is limited to a few kinds, or to their fibrous framework. The sponges are creatures of very low organization, concerning which controversies long raged, first as to whether they ought to be referred to the animal or the vegetable kingdom, and more recently as to their systematic position in the former group. At first referred to the Protozoa, and later to the Cælenterata (see ZOOLOGY), they are now considered by the greater number of naturalists as entitled to rank as a separate subkingdom, Porifera. characterized by the multitude of months or inhalent apertures which open through the body wall, the primitive mouth of the two-layered sac-like embryo being converted into the large exhalent opening.

They may be classified as follows: 1. Myxospongiæ destitute of skeleton; 2. Fibro-spongiæ, hating a fibrous skeleton, with or without siliceous spicules; 3. Calcispongiæ. having calcareous spicules. These spicules are not purely mineral, but contain a trace of organic matter. They are most beautiful microscopic objects, and spicules of different forms are sometimes found in the same species, sometimes lying close together in bundles, sometimes straight or slightly curved, sometimes in the shape of needles pointed at one end, or at both; sometimes of needles radiating from a center; whilst some have a head at one end, like a pin, some have grapnel-like hooks at the ends. Some of the species with horny framework have spicules imbedded in it; some have them implanted in the fibres; some are destitute of them. There is a beautiful West Indian species, Dictyocalyx pumiceus, in which the siliceous matter becomes itself a fibrous network, and is so fine and transparent as to resemble spun glass. In a living state, many sponges exhibit lively colors, from the presence of coloring matter.

Like any of the higher animals, the body of the sponge is com posed of a distinct outer layer of cells, the ectoderm or epidermis, and a ciliated inner layer or endoderm (often restricted to definite areas, the so-called ‘ ciliated chambers ‘), between which a middle layer of cells, the mesoderm arises. This may be of very variable thickness, and gives rise to the skeleton. From the close resemblance which the cells of the ectoderm and mesoderm present to Amœbæ, and those of the endoderm to those Infusorians known as Monads, it has been argued that the sponge is a mere colony of Protozoa. The development of the sponge, however, accords too closely with that of higher animals to admit of such a view, a free-swimming ciliated larva being produced by segmentation of a fertilized ovum; but it is undeniable that in the sponge we have a degree of independence of the cell units far greater than that which exists in any other group—a divided sponge readily re unites, and adjacent masses grow together. They assume very various forms, which, as well as the peculiarities in the structure of the framework, are characteristic of the different genera and species. Some are nearly globular; some cup-shaped, top-shaped, conical, cylindrical, thread-like, &c.; some are simple, and some branched.

The surface of a living sponge is generally covered with minute pores, through which water is imbibed, carrying with it both the air and the organic particles necessary for the support of life. The pores are supposed to be permanent in many of the sponges,

and the currents which enter through them to be produced by cilia, although these have as yet been detected only in a few species. But .in those of the very lowest organization, the pores seem to be formed for the occasion, just as the Amœba opens any where to admit food within its substance.

In Spongilla fluviatilis, a small fresh-water species found in Britain, the opening and closing of each pore occupies less than a minute, and the pores do not open simultaneously, but in irregular succession, and apparently never again in precisely the same spot. No trace of the pore remains for an instant after its closing, nor is there any indication of the point where a new one is to open. The water which enters by the pores passes out of some sponges by a single orifice, which serves for the whole mass; others have numerous orifices (oscula) which are permanent, and are much larger than the pores by which the water is imbibed, the whole mass being pervaded by canals which lead from the pores to these orifices, from which, under the microscope, a constant discharge of water may be seen taking place, minute opaque particles being carried along with its current. These particles are not only fecal matter, but gemmules and ova.

Reproduction takes place both by gemmation and by true ova. Many of the gemmules go to increase the sponge-mass; but the greater part finally become detached, and are carried out into the water, to settle down in a new locality Mr. Huxley has detected true ova and sperm-cells imbedded in the substance of sponges.

The sponges employed for domestic and other purposes derive their value from the elasticity and compressibility of their fibrous framework, divested of the glairy substance, and its power of imbibing fluids. The absence of spicules is essential to a useful sponge. The kinds fit for use are found in the seas of warm climates. Some small species of sponge live at great depths. One has been brought up in the Gulf of Macri from a depth of 185 fathoms. Numerous species of sponge are very abundant on many parts of the British coasts.

Fossil remains of sponges are found in many rocks, and of horny, fibrous kinds, as well as of those with calcareous or siliceous framework.

Several species of sponge are in use for economical purposes. Two species are chiefly brought from the Levant, and a very inferior one from the West Indies and coast of Florida. The trade in sponge is very considerable; it is carried on chiefly by the Turks and the inhabitants of the Bahama Islands. The number of men employed in the Ottoman sponge-fishery is between 4000 and 5000. forming the crews of about 600 boats. These boats find their chief employment on the coasts of Candia, Barbary, and Syria. The sponge is obtained by diving, the diver taking down with him a flat piece of stone of a triangular shape, with a hole drilled through one of its corners; to this a cord from the boat is attached, and the diver makes it serve to guide him to particular spots. When he reaches the growing sponges, he tears them off the rocks, and places them under his arms; he then pulls at the rope, which gives the signal to his companions in the boat to haul him up. The value of sponges collected in Greece and Turkey is from £90,000 to £100,000 annually. The Greeks of the Morea, instead of diving, obtain sponges by a pronged instrument; but the sponges thus collected are torn, and sell at a low price. The best sponges are obtained on detached heads of rock in 8 or 10 fathoms water.

The sponges of the Bahamas and other West Indian islands are of a larger size and coarser quality; but large quantities are gathered; and about 215,000 lbs., worth £17.000. are sent annually to Great Britain. The sponges are torn from the rocks by a fork at the end of a long pole. To get rid of the animal matter, they are buried for some days in the sand, and then soaked and washed.

The domestic uses of sponge are familiar to every one. It is also of great value to the surgeon, not only for removing blood in operations, but for checking hæmorrhage. Burnt sponge was once a valued remedy was scrofulous diseases and goitre; but iodine and bromine, from which it derives all its value, are now administered in other forms.