Reproduction takes place both by gemmation and by true ova. Many of the gem mules go on 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 sub stance, and its power of imbibing fluids. The absence of spicules is essential to a use ful 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.
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; is carried ou chiefly by the Turks and the inhabitants of the Bahama islands. The number of men employedin the Ottoman sponge-fishery is between 4,000 and 5,000. the crews of about 600 boats. These boats find their chief employment on the coast 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 Korea, instead of diving, obtain sponges by a pronged instrument; but the sponges thus coil acted 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 coarses 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. T..; get quit 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 hemorrhage. Burnt sponge was once a valid remedy for scrofulous diseases and goiter; but iodine and bromine, from which it derives all its value, are now administered in other forms.